Re: [RFC PATCH V4 08/17] x86/hyperv: Initialize cpu and memory for sev-snp enlightened guest

[Dave Hansen]

On 4/3/23 10:43, Tianyu Lan wrote:
> From: Tianyu Lan <tiala@xxxxxxxxxxxxx>
> 
> Read processor amd memory info from specific address which are
> populated by Hyper-V. Initialize smp cpu related ops, pvalidate
> system memory and add it into e820 table.
> 
> Signed-off-by: Tianyu Lan <tiala@xxxxxxxxxxxxx>
> ---
>  arch/x86/hyperv/ivm.c           | 78 +++++++++++++++++++++++++++++++++
>  arch/x86/include/asm/mshyperv.h | 16 +++++++
>  arch/x86/kernel/cpu/mshyperv.c  |  3 ++
>  3 files changed, 97 insertions(+)
> 
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index 368b2731950e..fa4de2761460 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -17,6 +17,11 @@
>  #include <asm/mem_encrypt.h>
>  #include <asm/mshyperv.h>
>  #include <asm/hypervisor.h>
> +#include <asm/coco.h>
> +#include <asm/io_apic.h>
> +#include <asm/sev.h>
> +#include <asm/realmode.h>
> +#include <asm/e820/api.h>
>  
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  
> @@ -57,6 +62,22 @@ union hv_ghcb {
>  
>  static u16 hv_ghcb_version __ro_after_init;
>  
> +static u32 processor_count;
> +
> +static __init void hv_snp_get_smp_config(unsigned int early)
> +{
> +	if (!early) {
> +		while (num_processors < processor_count) {
> +			early_per_cpu(x86_cpu_to_apicid, num_processors) = num_processors;
> +			early_per_cpu(x86_bios_cpu_apicid, num_processors) = num_processors;
> +			physid_set(num_processors, phys_cpu_present_map);
> +			set_cpu_possible(num_processors, true);
> +			set_cpu_present(num_processors, true);
> +			num_processors++;
> +		}
> +	}
> +}

Folks, please minimize indentation:

	if (early)
		return;

It would also be nice to see *some* explanation in the changelog or
comments about why it's best and correct to just do nothing if early==1.

Also, this _consumes_ data from hv_sev_init_mem_and_cpu().  It would
make more sense to me to have them ordered the other way.
hv_sev_init_mem_and_cpu() first, this second.

>  u64 hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_size)
>  {
>  	union hv_ghcb *hv_ghcb;
> @@ -356,6 +377,63 @@ static bool hv_is_private_mmio(u64 addr)
>  	return false;
>  }
>  
> +__init void hv_sev_init_mem_and_cpu(void)
> +{
> +	struct memory_map_entry *entry;
> +	struct e820_entry *e820_entry;
> +	u64 e820_end;
> +	u64 ram_end;
> +	u64 page;
> +
> +	/*
> +	 * Hyper-V enlightened snp guest boots kernel
> +	 * directly without bootloader and so roms,
> +	 * bios regions and reserve resources are not
> +	 * available. Set these callback to NULL.
> +	 */
> +	x86_platform.legacy.reserve_bios_regions = 0;
> +	x86_init.resources.probe_roms = x86_init_noop;
> +	x86_init.resources.reserve_resources = x86_init_noop;
> +	x86_init.mpparse.find_smp_config = x86_init_noop;
> +	x86_init.mpparse.get_smp_config = hv_snp_get_smp_config;

This is one of those places that vertical alignment adds clarity:

> +	x86_init.resources.probe_roms	     = x86_init_noop;
> +	x86_init.resources.reserve_resources = x86_init_noop;
> +	x86_init.mpparse.find_smp_config     = x86_init_noop;
> +	x86_init.mpparse.get_smp_config      = hv_snp_get_smp_config;

See? 3 noops and only one actual implemented function.  Clear as day now.

> +	/*> +	 * Hyper-V SEV-SNP enlightened guest doesn't support ioapic
> +	 * and legacy APIC page read/write. Switch to hv apic here.
> +	 */
> +	disable_ioapic_support();

Do these systems have X86_FEATURE_APIC set?  Why is this needed in
addition to the architectural enumeration that already exists?

Is there any other place in the kernel that has this one-off disabling
of the APIC?

> +	/* Read processor number and memory layout. */
> +	processor_count = *(u32 *)__va(EN_SEV_SNP_PROCESSOR_INFO_ADDR);
> +	entry = (struct memory_map_entry *)(__va(EN_SEV_SNP_PROCESSOR_INFO_ADDR)
> +			+ sizeof(struct memory_map_entry));

Ick.

There are a lot of ways to do this.  But, this is an awfully ugly way.

struct snp_processor_info {
	u32 processor_count;
	struct memory_map_entry[] entries;
}

struct snp_processor_info *snp_pi =
				__va(EN_SEV_SNP_PROCESSOR_INFO_ADDR);
processor_count = snp_pi->processor_count;

Then, have your for() loop through snp_pi->entries;

Actually, I'm not _quite_ sure that processor_count and entries are next
to each other.  But, either way, I do think a struct makes sense.

Also, what guarantees that EN_SEV_SNP_PROCESSOR_INFO_ADDR is mapped?
It's up above 8MB which I don't remember off the top of my head as being
a special address.

> +	/*
> +	 * E820 table in the memory just describes memory for
> +	 * kernel, ACPI table, cmdline, boot params and ramdisk.
> +	 * Hyper-V popoulates the rest memory layout in the EN_SEV_
> +	 * SNP_PROCESSOR_INFO_ADDR.
> +	 */

Really?  That is not very cool.  We need a better explanation of why
there was no way to use the decades-old e820 or EFI memory map and why
this needs to be a special snowflake.

> +	for (; entry->numpages != 0; entry++) {
> +		e820_entry = &e820_table->entries[
> +				e820_table->nr_entries - 1];
> +		e820_end = e820_entry->addr + e820_entry->size;
> +		ram_end = (entry->starting_gpn +
> +			   entry->numpages) * PAGE_SIZE;
> +
> +		if (e820_end < entry->starting_gpn * PAGE_SIZE)
> +			e820_end = entry->starting_gpn * PAGE_SIZE;
> +
> +		if (e820_end < ram_end) {
> +			pr_info("Hyper-V: add e820 entry [mem %#018Lx-%#018Lx]\n", e820_end, ram_end - 1);
> +			e820__range_add(e820_end, ram_end - e820_end,
> +					E820_TYPE_RAM);
> +			for (page = e820_end; page < ram_end; page += PAGE_SIZE)
> +				pvalidate((unsigned long)__va(page), RMP_PG_SIZE_4K, true);
> +		}
> +	}
> +}

Oh, is this just about having a pre-accepted area and a non-accepted
area?  Is this basically another one-off implementation of unaccepted
memory ... that doesn't use the EFI standard?

>  void __init hv_vtom_init(void)
>  {
>  	/*
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 3c15e23162e7..a4a59007b5f2 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -41,6 +41,20 @@ extern bool hv_isolation_type_en_snp(void);
>  
>  extern union hv_ghcb * __percpu *hv_ghcb_pg;
>  
> +/*
> + * Hyper-V puts processor and memory layout info
> + * to this address in SEV-SNP enlightened guest.
> + */
> +#define EN_SEV_SNP_PROCESSOR_INFO_ADDR 0x802000
> +
> +struct memory_map_entry {
> +	u64 starting_gpn;
> +	u64 numpages;
> +	u16 type;
> +	u16 flags;
> +	u32 reserved;
> +};
> +
>  int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
>  int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
>  int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
> @@ -246,12 +260,14 @@ void hv_ghcb_msr_read(u64 msr, u64 *value);
>  bool hv_ghcb_negotiate_protocol(void);
>  void hv_ghcb_terminate(unsigned int set, unsigned int reason);
>  void hv_vtom_init(void);
> +void hv_sev_init_mem_and_cpu(void);
>  #else
>  static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
>  static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
>  static inline bool hv_ghcb_negotiate_protocol(void) { return false; }
>  static inline void hv_ghcb_terminate(unsigned int set, unsigned int reason) {}
>  static inline void hv_vtom_init(void) {}
> +static inline void hv_sev_init_mem_and_cpu(void) {}
>  #endif
>  
>  extern bool hv_isolation_type_snp(void);
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 2f2dcb2370b6..71820bbf9e90 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -529,6 +529,9 @@ static void __init ms_hyperv_init_platform(void)
>  	if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT))
>  		mark_tsc_unstable("running on Hyper-V");
>  
> +	if (hv_isolation_type_en_snp())
> +		hv_sev_init_mem_and_cpu();
> +
>  	hardlockup_detector_disable();
>  }
>