RE: [PATCH v3 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk

[JeeHeng Sia]

> -----Original Message-----
> From: Alexandre Ghiti <alex@xxxxxxxx>
> Sent: Tuesday, 7 February, 2023 11:46 PM
> To: JeeHeng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>; paul.walmsley@xxxxxxxxxx; palmer@xxxxxxxxxxx; aou@xxxxxxxxxxxxxxxxx
> Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Leyfoon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>; Mason Huo
> <mason.huo@xxxxxxxxxxxxxxxx>
> Subject: Re: [PATCH v3 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk
> 
> Hi Sia,
> 
> On 1/27/23 10:10, Sia Jee Heng wrote:
> > Low level Arch functions were created to support hibernation.
> > swsusp_arch_suspend() relies code from __cpu_suspend_enter() to write
> > cpu state onto the stack, then calling swsusp_save() to save the memory
> > image.
> >
> > Arch specific hibernation header is implemented and is utilized by the
> > arch_hibernation_header_restore() and arch_hibernation_header_save()
> > functions. The arch specific hibernation header consists of satp, hartid,
> > and the cpu_resume address. The kernel built version is also need to be
> > saved into the hibernation image header to making sure only the same
> > kernel is restore when resume.
> >
> > swsusp_arch_resume() creates a temporary page table that covering only
> > the linear map. It copies the restore code to a 'safe' page, then start
> > to restore the memory image. Once completed, it restores the original
> > kernel's page table. It then calls into __hibernate_cpu_resume()
> > to restore the CPU context. Finally, it follows the normal hibernation
> > path back to the hibernation core.
> >
> > To enable hibernation/suspend to disk into RISCV, the below config
> > need to be enabled:
> > - CONFIG_ARCH_HIBERNATION_HEADER
> > - CONFIG_ARCH_HIBERNATION_POSSIBLE
> >
> > Signed-off-by: Sia Jee Heng <jeeheng.sia@xxxxxxxxxxxxxxxx>
> > Reviewed-by: Ley Foon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>
> > Reviewed-by: Mason Huo <mason.huo@xxxxxxxxxxxxxxxx>
> > ---
> >   arch/riscv/Kconfig                 |   7 +
> >   arch/riscv/include/asm/assembler.h |  20 ++
> >   arch/riscv/include/asm/suspend.h   |  21 ++
> >   arch/riscv/kernel/Makefile         |   1 +
> >   arch/riscv/kernel/asm-offsets.c    |   5 +
> >   arch/riscv/kernel/hibernate-asm.S  |  89 +++++++
> >   arch/riscv/kernel/hibernate.c      | 360 +++++++++++++++++++++++++++++
> >   7 files changed, 503 insertions(+)
> >   create mode 100644 arch/riscv/kernel/hibernate-asm.S
> >   create mode 100644 arch/riscv/kernel/hibernate.c
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index e2b656043abf..4555848a817f 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -690,6 +690,13 @@ menu "Power management options"
> >
> >   source "kernel/power/Kconfig"
> >
> > +config ARCH_HIBERNATION_POSSIBLE
> > +	def_bool y
> > +
> > +config ARCH_HIBERNATION_HEADER
> > +	def_bool y
> > +	depends on HIBERNATION
> > +
> >   endmenu # "Power management options"
> >
> >   menu "CPU Power Management"
> > diff --git a/arch/riscv/include/asm/assembler.h b/arch/riscv/include/asm/assembler.h
> > index ef1283d04b70..3de70d3e6ceb 100644
> > --- a/arch/riscv/include/asm/assembler.h
> > +++ b/arch/riscv/include/asm/assembler.h
> > @@ -59,4 +59,24 @@
> >   		REG_L	s11, (SUSPEND_CONTEXT_REGS + PT_S11)(a0)
> >   	.endm
> >
> > +/**
> > + * copy_page - copy 1 page (4KB) of data from source to destination
> > + * @a0 - destination
> > + * @a1 - source
> > + */
> > +	.macro	copy_page a0, a1
> > +		lui	a2, 0x1
> > +		add	a2, a2, a0
> > +.1 :
> > +		REG_L	t0, 0(a1)
> > +		REG_L	t1, SZREG(a1)
> > +
> > +		REG_S	t0, 0(a0)
> > +		REG_S	t1, SZREG(a0)
> > +
> > +		addi	a0, a0, 2 * SZREG
> > +		addi	a1, a1, 2 * SZREG
> > +		bne	a2, a0, .1
> > +	.endm
> > +
> >   #endif	/* __ASM_ASSEMBLER_H */
> > diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
> > index 75419c5ca272..db40ae433aa9 100644
> > --- a/arch/riscv/include/asm/suspend.h
> > +++ b/arch/riscv/include/asm/suspend.h
> > @@ -21,6 +21,12 @@ struct suspend_context {
> >   #endif
> >   };
> >
> > +/*
> > + * This parameter will be assigned to 0 during resume and will be used by
> > + * hibernation core for the subsequent resume sequence
> > + */
> > +extern int in_suspend;
> > +
> >   /* Low-level CPU suspend entry function */
> >   int __cpu_suspend_enter(struct suspend_context *context);
> >
> > @@ -36,4 +42,19 @@ int __cpu_resume_enter(unsigned long hartid, unsigned long context);
> >   /* Used to save and restore the csr */
> >   void suspend_save_csrs(struct suspend_context *context);
> >   void suspend_restore_csrs(struct suspend_context *context);
> > +
> > +/* Low-level API to support hibernation */
> > +int swsusp_arch_suspend(void);
> > +int swsusp_arch_resume(void);
> > +int arch_hibernation_header_save(void *addr, unsigned int max_size);
> > +int arch_hibernation_header_restore(void *addr);
> > +int __hibernate_cpu_resume(void);
> > +
> > +/* Used to resume on the CPU we hibernated on */
> > +int hibernate_resume_nonboot_cpu_disable(void);
> > +
> > +/* Used to restore the hibernated image */
> > +asmlinkage void restore_image(unsigned long resume_satp, unsigned long satp_temp,
> > +				unsigned long cpu_resume);
> > +asmlinkage int core_restore_code(void);
> >   #endif
> > diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> > index 4cf303a779ab..daab341d55e4 100644
> > --- a/arch/riscv/kernel/Makefile
> > +++ b/arch/riscv/kernel/Makefile
> > @@ -64,6 +64,7 @@ obj-$(CONFIG_MODULES)		+= module.o
> >   obj-$(CONFIG_MODULE_SECTIONS)	+= module-sections.o
> >
> >   obj-$(CONFIG_CPU_PM)		+= suspend_entry.o suspend.o
> > +obj-$(CONFIG_HIBERNATION)	+= hibernate.o hibernate-asm.o
> >
> >   obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
> >   obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
> > diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> > index df9444397908..d6a75aac1d27 100644
> > --- a/arch/riscv/kernel/asm-offsets.c
> > +++ b/arch/riscv/kernel/asm-offsets.c
> > @@ -9,6 +9,7 @@
> >   #include <linux/kbuild.h>
> >   #include <linux/mm.h>
> >   #include <linux/sched.h>
> > +#include <linux/suspend.h>
> >   #include <asm/kvm_host.h>
> >   #include <asm/thread_info.h>
> >   #include <asm/ptrace.h>
> > @@ -116,6 +117,10 @@ void asm_offsets(void)
> >
> >   	OFFSET(SUSPEND_CONTEXT_REGS, suspend_context, regs);
> >
> > +	OFFSET(HIBERN_PBE_ADDR, pbe, address);
> > +	OFFSET(HIBERN_PBE_ORIG, pbe, orig_address);
> > +	OFFSET(HIBERN_PBE_NEXT, pbe, next);
> > +
> >   	OFFSET(KVM_ARCH_GUEST_ZERO, kvm_vcpu_arch, guest_context.zero);
> >   	OFFSET(KVM_ARCH_GUEST_RA, kvm_vcpu_arch, guest_context.ra);
> >   	OFFSET(KVM_ARCH_GUEST_SP, kvm_vcpu_arch, guest_context.sp);
> > diff --git a/arch/riscv/kernel/hibernate-asm.S b/arch/riscv/kernel/hibernate-asm.S
> > new file mode 100644
> > index 000000000000..a83d534b89bd
> > --- /dev/null
> > +++ b/arch/riscv/kernel/hibernate-asm.S
> > @@ -0,0 +1,89 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Hibernation support specific for RISCV
> > + *
> > + * Copyright (C) 2023 StarFive Technology Co., Ltd.
> > + *
> > + * Author: Jee Heng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>
> > + */
> > +
> > +#include <asm/asm.h>
> > +#include <asm/asm-offsets.h>
> > +#include <asm/assembler.h>
> > +#include <asm/csr.h>
> > +
> > +#include <linux/linkage.h>
> > +
> > +/*
> > + * This code is executed when resume from the hibernation.
> > + *
> > + * It begins with loading the temporary page table then restores the memory image.
> > + * Finally branches to __hibernate_cpu_resume() to restore the state saved by
> > + * swsusp_arch_suspend().
> > + */
> > +
> > +/*
> > + * int __hibernate_cpu_resume(void)
> > + * Switch back to the hibernated image's page table prior to restore the CPU
> > + * context.
> > + *
> > + * Always returns 0 to the C code.
> > + */
> > +ENTRY(__hibernate_cpu_resume)
> > +	/* switch to hibernated image's page table */
> > +	csrw CSR_SATP, s0
> > +	sfence.vma
> > +
> > +	REG_L	a0, hibernate_cpu_context
> > +
> > +	/* Restore CSRs */
> > +	restore_csr
> > +
> > +	/* Restore registers (except A0 and T0-T6) */
> > +	restore_reg
> > +
> > +	/* Return zero value */
> > +	add	a0, zero, zero
> > +
> > +	/* Return to C code */
> > +	ret
> > +END(__hibernate_cpu_resume)
> > +
> > +/*
> > + * Prepare to restore the image.
> > + * a0: satp of saved page tables
> > + * a1: satp of temporary page tables
> > + * a2: cpu_resume
> > + */
> > +ENTRY(restore_image)
> > +	mv	s0, a0
> > +	mv	s1, a1
> > +	mv	s2, a2
> > +	REG_L	s4, restore_pblist
> > +	REG_L	a1, relocated_restore_code
> > +
> > +	jalr	a1
> > +END(restore_image)
> > +
> > +/*
> > + * The below code will be executed from a 'safe' page.
> > + * It first switches to the temporary page table, then start to copy the pages
> > + * back to the original memory location. Finally, it jumps to the __hibernate_cpu_resume()
> > + * to restore the CPU context.
> > + */
> > +ENTRY(core_restore_code)
> > +	/* switch to temp page table */
> > +	csrw satp, s1
> > +	sfence.vma
> > +.Lcopy:
> > +	/* The below code will restore the hibernated image. */
> > +	REG_L	a1, HIBERN_PBE_ADDR(s4)
> > +	REG_L	a0, HIBERN_PBE_ORIG(s4)
> > +
> > +	copy_page a0, a1
> > +
> > +	REG_L	s4, HIBERN_PBE_NEXT(s4)
> > +	bnez	s4, .Lcopy
> > +
> > +	jalr	s2
> > +END(core_restore_code)
> > diff --git a/arch/riscv/kernel/hibernate.c b/arch/riscv/kernel/hibernate.c
> > new file mode 100644
> > index 000000000000..bf7f3c781820
> > --- /dev/null
> > +++ b/arch/riscv/kernel/hibernate.c
> > @@ -0,0 +1,360 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Hibernation support specific for RISCV
> > + *
> > + * Copyright (C) 2023 StarFive Technology Co., Ltd.
> > + *
> > + * Author: Jee Heng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>
> > + */
> > +
> > +#include <asm/barrier.h>
> > +#include <asm/cacheflush.h>
> > +#include <asm/mmu_context.h>
> > +#include <asm/page.h>
> > +#include <asm/pgtable.h>
> > +#include <asm/sections.h>
> > +#include <asm/set_memory.h>
> > +#include <asm/smp.h>
> > +#include <asm/suspend.h>
> > +
> > +#include <linux/cpu.h>
> > +#include <linux/memblock.h>
> > +#include <linux/pm.h>
> > +#include <linux/sched.h>
> > +#include <linux/suspend.h>
> > +#include <linux/utsname.h>
> > +
> > +/* The logical cpu number we should resume on, initialised to a non-cpu number */
> > +static int sleep_cpu = -EINVAL;
> > +
> > +/* CPU context to be saved */
> > +struct suspend_context *hibernate_cpu_context;
> > +
> > +unsigned long relocated_restore_code;
> > +
> > +/* Pointer to the temporary resume page table */
> > +pgd_t *resume_pg_dir;
> > +
> > +/**
> > + * struct arch_hibernate_hdr_invariants - container to store kernel build version
> > + * @uts_version: to save the build number and date so that the we are not resume with
> > + *		a different kernel
> > + */
> > +struct arch_hibernate_hdr_invariants {
> > +	char		uts_version[__NEW_UTS_LEN + 1];
> > +};
> > +
> > +/**
> > + * struct arch_hibernate_hdr - helper parameters that help us to restore the image
> > + * @invariants: container to store kernel build version
> > + * @hartid: to make sure same boot_cpu executing the hibernate/restore code.
> > + * @saved_satp: original page table used by the hibernated image.
> > + * @restore_cpu_addr: the kernel's image address to restore the CPU context.
> > + */
> > +static struct arch_hibernate_hdr {
> > +	struct arch_hibernate_hdr_invariants invariants;
> > +	unsigned long	hartid;
> > +	unsigned long	saved_satp;
> > +	unsigned long	restore_cpu_addr;
> > +} resume_hdr;
> > +
> > +static inline void arch_hdr_invariants(struct arch_hibernate_hdr_invariants *i)
> > +{
> > +	memset(i, 0, sizeof(*i));
> > +	memcpy(i->uts_version, init_utsname()->version, sizeof(i->uts_version));
> > +}
> > +
> > +/*
> > + * Check if the given pfn is in the 'nosave' section.
> > + */
> > +int pfn_is_nosave(unsigned long pfn)
> > +{
> > +	unsigned long nosave_begin_pfn = sym_to_pfn(&__nosave_begin);
> > +	unsigned long nosave_end_pfn = sym_to_pfn(&__nosave_end - 1);
> > +
> > +	return ((pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn));
> > +}
> > +
> > +void notrace save_processor_state(void)
> > +{
> > +	WARN_ON(num_online_cpus() != 1);
> > +}
> > +
> > +void notrace restore_processor_state(void)
> > +{
> > +}
> > +
> > +/*
> > + * Helper parameters need to be saved to the hibernation image header.
> > + */
> > +int arch_hibernation_header_save(void *addr, unsigned int max_size)
> > +{
> > +	struct arch_hibernate_hdr *hdr = addr;
> > +
> > +	if (max_size < sizeof(*hdr))
> > +		return -EOVERFLOW;
> > +
> > +	arch_hdr_invariants(&hdr->invariants);
> > +
> > +	hdr->hartid = cpuid_to_hartid_map(sleep_cpu);
> > +	hdr->saved_satp = csr_read(CSR_SATP);
> > +	hdr->restore_cpu_addr = (unsigned long)__hibernate_cpu_resume;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(arch_hibernation_header_save);
> > +
> > +/*
> > + * Retrieve the helper parameters from the hibernation image header
> > + */
> > +int arch_hibernation_header_restore(void *addr)
> > +{
> > +	struct arch_hibernate_hdr_invariants invariants;
> > +	struct arch_hibernate_hdr *hdr = addr;
> > +	int ret = 0;
> > +
> > +	arch_hdr_invariants(&invariants);
> > +
> > +	if (memcmp(&hdr->invariants, &invariants, sizeof(invariants))) {
> > +		pr_crit("Hibernate image not generated by this kernel!\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	sleep_cpu = riscv_hartid_to_cpuid(hdr->hartid);
> > +	if (sleep_cpu < 0) {
> > +		pr_crit("Hibernated on a CPU not known to this kernel!\n");
> > +		sleep_cpu = -EINVAL;
> > +		return -EINVAL;
> > +	}
> > +
> > +#ifdef CONFIG_SMP
> > +	ret = bringup_hibernate_cpu(sleep_cpu);
> > +	if (ret) {
> > +		sleep_cpu = -EINVAL;
> > +		return ret;
> > +	}
> > +#endif
> > +	resume_hdr = *hdr;
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL(arch_hibernation_header_restore);
> > +
> > +int swsusp_arch_suspend(void)
> > +{
> > +	int ret = 0;
> > +
> > +	if (__cpu_suspend_enter(hibernate_cpu_context)) {
> > +		sleep_cpu = smp_processor_id();
> > +		suspend_save_csrs(hibernate_cpu_context);
> > +		ret = swsusp_save();
> > +	} else {
> > +		suspend_restore_csrs(hibernate_cpu_context);
> > +		flush_tlb_all();
> > +
> > +		/* Invalidated Icache */
> > +		flush_icache_all();
> > +
> > +		/*
> > +		 * Tell the hibernation core that we've just restored
> > +		 * the memory
> > +		 */
> > +		in_suspend = 0;
> > +		sleep_cpu = -EINVAL;
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +static unsigned long temp_pgtable_map_pte(pte_t *ptep, unsigned long vaddr, pgprot_t prot)
> > +{
> > +	uintptr_t pte_idx = pte_index(vaddr);
> > +
> > +	ptep[pte_idx] = pfn_pte(PFN_DOWN(__pa(vaddr)), prot);
> > +
> > +	return 0;
> > +}
> > +
> > +#ifndef __PAGETABLE_PMD_FOLDED
> > +#define temp_pgtable_map_pgd_next(pgdp, vaddr, prot)			\
> > +		(pgtable_l5_enabled ?					\
> > +		temp_pgtable_map_p4d(pgdp, vaddr, prot) :		\
> > +		(pgtable_l4_enabled ?					\
> > +		temp_pgtable_map_pud((pud_t *)pgdp, vaddr, prot) :	\
> > +		temp_pgtable_map_pmd((pmd_t *)pgdp, vaddr, prot)))
> > +
> > +static unsigned long temp_pgtable_map_pmd(pmd_t *pmdp, unsigned long vaddr, pgprot_t prot)
> > +{
> > +	uintptr_t pmd_idx = pmd_index(vaddr);
> > +	pte_t *ptep;
> > +
> > +	if (pmd_none(pmdp[pmd_idx])) {
> > +		ptep = (pte_t *)get_safe_page(GFP_ATOMIC);
> > +		if (!ptep)
> > +			return -ENOMEM;
> > +
> > +		memset(ptep, 0, PAGE_SIZE);
> > +		pmdp[pmd_idx] = pfn_pmd(PFN_DOWN(__pa(ptep)), PAGE_TABLE);
> > +	} else {
> > +		ptep = (pte_t *)__va(PFN_PHYS(_pmd_pfn(pmdp[pmd_idx])));
> > +	}
> > +
> > +	return temp_pgtable_map_pte(ptep, vaddr, prot);
> > +}
> > +
> > +static unsigned long temp_pgtable_map_pud(pud_t *pudp, unsigned long vaddr, pgprot_t prot)
> > +{
> > +	uintptr_t pud_index = pud_index(vaddr);
> > +	pmd_t *pmdp;
> > +
> > +	if (pud_val(pudp[pud_index]) == 0) {
> > +		pmdp = (pmd_t *)get_safe_page(GFP_ATOMIC);
> > +		if (!pmdp)
> > +			return -ENOMEM;
> > +
> > +		memset(pmdp, 0, PAGE_SIZE);
> > +		pudp[pud_index] = pfn_pud(PFN_DOWN(__pa(pmdp)), PAGE_TABLE);
> > +	} else {
> > +		pmdp = (pmd_t *)__va(PFN_PHYS(_pud_pfn(pudp[pud_index])));
> > +	}
> > +
> > +	return temp_pgtable_map_pmd(pmdp, vaddr, prot);
> > +}
> > +
> > +static unsigned long temp_pgtable_map_p4d(p4d_t *p4dp, unsigned long vaddr, pgprot_t prot)
> > +{
> > +	uintptr_t p4d_index = p4d_index(vaddr);
> > +	pud_t *pudp;
> > +
> > +	if (p4d_val(p4dp[p4d_index]) == 0) {
> > +		pudp = (pud_t *)get_safe_page(GFP_ATOMIC);
> > +		if (!pudp)
> > +			return -ENOMEM;
> > +
> > +		memset(pudp, 0, PAGE_SIZE);
> > +		p4dp[p4d_index] = pfn_p4d(PFN_DOWN(__pa(pudp)), PAGE_TABLE);
> > +	} else {
> > +		pudp = (pud_t *)__va(PFN_PHYS(_p4d_pfn(p4dp[p4d_index])));
> > +	}
> > +
> > +	return temp_pgtable_map_pud(pudp, vaddr, prot);
> > +}
> > +
> > +#else
> > +#define temp_pgtable_map_pgd_next(nextp, vaddr, prot)	\
> > +	temp_pgtable_map_pte((pte_t *)nextp, vaddr, prot)
> > +#endif /* __PAGETABLE_PMD_FOLDED */
> > +
> > +static unsigned long temp_pgtable_map_pgd(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
> > +{
> > +	uintptr_t pgd_idx = pgd_index(vaddr);
> > +	void *nextp;
> > +
> > +	if (pgd_val(pgdp[pgd_idx]) == 0) {
> > +		nextp = (void *)get_safe_page(GFP_ATOMIC);
> > +		if (!nextp)
> > +			return -ENOMEM;
> > +
> > +		memset(nextp, 0, PAGE_SIZE);
> > +		pgdp[pgd_idx] = pfn_pgd(PFN_DOWN(__pa(nextp)), PAGE_TABLE);
> > +	} else {
> > +		nextp = (void *)__va(PFN_PHYS(_pgd_pfn(pgdp[pgd_idx])));
> > +	}
> > +
> > +	return temp_pgtable_map_pgd_next(nextp, vaddr, prot);
> > +}
> > +
> > +static unsigned long temp_pgtable_mapping(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
> > +{
> > +	return temp_pgtable_map_pgd(pgdp, vaddr, prot);
> > +}
> > +
> > +static unsigned long relocate_restore_code(void)
> > +{
> > +	unsigned long ret;
> > +	void *page = (void *)get_safe_page(GFP_ATOMIC);
> > +
> > +	if (!page)
> > +		return -ENOMEM;
> > +
> > +	copy_page(page, core_restore_code);
> > +
> > +	/* Make the page containing the relocated code executable */
> > +	set_memory_x((unsigned long)page, 1);
> > +
> > +	ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)page, PAGE_KERNEL_READ_EXEC);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return (unsigned long)page;
> > +}
> > +
> > +int swsusp_arch_resume(void)
> > +{
> > +	unsigned long addr = PAGE_OFFSET;
> > +	unsigned long ret;
> > +
> > +	/*
> > +	 * Memory allocated by get_safe_page() will be dealt with by the hibernation core,
> > +	 * we don't need to free it here.
> > +	 */
> > +	resume_pg_dir = (pgd_t *)get_safe_page(GFP_ATOMIC);
> > +	if (!resume_pg_dir)
> > +		return -ENOMEM;
> > +
> > +	/*
> > +	 * The pages need to be writable when restoring the image.
> > +	 * Create a second copy of page table just for the linear map, and use this when
> > +	 * restoring.
> > +	 */
> > +	for (; addr <= (unsigned long)pfn_to_virt(max_low_pfn); addr += PAGE_SIZE) {
> > +		ret = temp_pgtable_mapping(resume_pg_dir, addr, PAGE_KERNEL);
> > +		if (ret)
> > +			return (int)ret;
> > +	}
> > +
> 
> 
> To me this is wrong as this does not account for the real physical
> mapping layout: can't you simply copy the linear mapping from
> swapper_pg_dir?
Hi, we covering the linear mapping from PAGE_OFFSET up to pfn_to_virt(max_low_pfn). We shouldn't copy from the swapper_pg_dir as we are not suppose to modify its content.
> 
> But I have to admit that I struggle to understand the need for this
> temporary page table: all we need to do is to allow to write to the
> linear mapping, so why don't we simply set_memory_rw(linear mapping)?
Similar to the above comment. When we restore the memory content, we need to make sure the pages are write-able. if you modify the swapper_pg_dir, the kernel will crash afterwards.
That’s why we need a second page table to do the recovering job.
> 
> 
> > +	/* Move the restore code to a new page so that it doesn't get overwritten by itself */
> > +	relocated_restore_code = relocate_restore_code();
> 
> 
> And do we really need to do that too? The code in question can only be
> overwritten by the same code right?
Yes, we need to move the recovering code to a new page to prevent the code from overwrite itself when restoring the memory.
> 
> Thanks,
> 
> Alex
> 
> 
> > +	if (relocated_restore_code == -ENOMEM)
> > +		return -ENOMEM;
> > +
> > +	/*
> > +	 * Map the __hibernate_cpu_resume() address to the temporary page table so that the
> > +	 * restore code can jump to it after finished restore the image. The next execution
> > +	 * code doesn't find itself in a different address space after switching over to the
> > +	 * original page table used by the hibernated image.
> > +	 */
> > +	ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)resume_hdr.restore_cpu_addr,
> > +					PAGE_KERNEL_READ_EXEC);
> > +	if (ret)
> > +		return ret;
> > +
> > +	restore_image(resume_hdr.saved_satp, (PFN_DOWN(__pa(resume_pg_dir)) | satp_mode),
> > +			resume_hdr.restore_cpu_addr);
> > +
> > +	return 0;
> > +}
> > +
> > +#ifdef CONFIG_PM_SLEEP_SMP
> > +int hibernate_resume_nonboot_cpu_disable(void)
> > +{
> > +	if (sleep_cpu < 0) {
> > +		pr_err("Failing to resume from hibernate on an unknown CPU.\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	return freeze_secondary_cpus(sleep_cpu);
> > +}
> > +#endif
> > +
> > +static int __init riscv_hibernate_init(void)
> > +{
> > +	hibernate_cpu_context = kcalloc(1, sizeof(struct suspend_context), GFP_KERNEL);
> > +
> > +	if (WARN_ON(!hibernate_cpu_context))
> > +		return -ENOMEM;
> > +
> > +	return 0;
> > +}
> > +
> > +early_initcall(riscv_hibernate_init);