Re: [PATCH v4 4/6] LoongArch: Add paravirt interface for guest kernel

[Huacai Chen]

Hi, Bibo,

On Thu, Feb 1, 2024 at 11:19 AM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>
> The patch adds paravirt interface for guest kernel, function
> pv_guest_initi() firstly checks whether system runs on VM mode. If kernel
> runs on VM mode, it will call function kvm_para_available() to detect
> whether current VMM is KVM hypervisor. And the paravirt function can work
> only if current VMM is KVM hypervisor, since there is only KVM hypervisor
> supported on LoongArch now.
>
> This patch only adds paravirt interface for guest kernel, however there
> is not effective pv functions added here.
>
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
>  arch/loongarch/Kconfig                        |  9 ++++
>  arch/loongarch/include/asm/kvm_para.h         |  7 ++++
>  arch/loongarch/include/asm/paravirt.h         | 27 ++++++++++++
>  .../include/asm/paravirt_api_clock.h          |  1 +
>  arch/loongarch/kernel/Makefile                |  1 +
>  arch/loongarch/kernel/paravirt.c              | 41 +++++++++++++++++++
>  arch/loongarch/kernel/setup.c                 |  2 +
>  7 files changed, 88 insertions(+)
>  create mode 100644 arch/loongarch/include/asm/paravirt.h
>  create mode 100644 arch/loongarch/include/asm/paravirt_api_clock.h
>  create mode 100644 arch/loongarch/kernel/paravirt.c
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 10959e6c3583..817a56dff80f 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -585,6 +585,15 @@ config CPU_HAS_PREFETCH
>         bool
>         default y
>
> +config PARAVIRT
> +       bool "Enable paravirtualization code"
> +       depends on AS_HAS_LVZ_EXTENSION
> +       help
> +          This changes the kernel so it can modify itself when it is run
> +         under a hypervisor, potentially improving performance significantly
> +         over full virtualization.  However, when run without a hypervisor
> +         the kernel is theoretically slower and slightly larger.
> +
>  config ARCH_SUPPORTS_KEXEC
>         def_bool y
>
> diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
> index 9425d3b7e486..41200e922a82 100644
> --- a/arch/loongarch/include/asm/kvm_para.h
> +++ b/arch/loongarch/include/asm/kvm_para.h
> @@ -2,6 +2,13 @@
>  #ifndef _ASM_LOONGARCH_KVM_PARA_H
>  #define _ASM_LOONGARCH_KVM_PARA_H
>
> +/*
> + * Hypcall code field
> + */
> +#define HYPERVISOR_KVM                 1
> +#define HYPERVISOR_VENDOR_SHIFT                8
> +#define HYPERCALL_CODE(vendor, code)   ((vendor << HYPERVISOR_VENDOR_SHIFT) + code)
> +
>  /*
>   * LoongArch hypcall return code
>   */
> diff --git a/arch/loongarch/include/asm/paravirt.h b/arch/loongarch/include/asm/paravirt.h
> new file mode 100644
> index 000000000000..b64813592ba0
> --- /dev/null
> +++ b/arch/loongarch/include/asm/paravirt.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_LOONGARCH_PARAVIRT_H
> +#define _ASM_LOONGARCH_PARAVIRT_H
> +
> +#ifdef CONFIG_PARAVIRT
> +#include <linux/static_call_types.h>
> +struct static_key;
> +extern struct static_key paravirt_steal_enabled;
> +extern struct static_key paravirt_steal_rq_enabled;
> +
> +u64 dummy_steal_clock(int cpu);
> +DECLARE_STATIC_CALL(pv_steal_clock, dummy_steal_clock);
> +
> +static inline u64 paravirt_steal_clock(int cpu)
> +{
> +       return static_call(pv_steal_clock)(cpu);
> +}
The steal time code can be removed in this patch, I think.

> +
> +int pv_guest_init(void);
> +#else
> +static inline int pv_guest_init(void)
> +{
> +       return 0;
> +}
> +
> +#endif // CONFIG_PARAVIRT
> +#endif
> diff --git a/arch/loongarch/include/asm/paravirt_api_clock.h b/arch/loongarch/include/asm/paravirt_api_clock.h
> new file mode 100644
> index 000000000000..65ac7cee0dad
> --- /dev/null
> +++ b/arch/loongarch/include/asm/paravirt_api_clock.h
> @@ -0,0 +1 @@
> +#include <asm/paravirt.h>
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index 3c808c680370..662e6e9de12d 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -48,6 +48,7 @@ obj-$(CONFIG_MODULES)         += module.o module-sections.o
>  obj-$(CONFIG_STACKTRACE)       += stacktrace.o
>
>  obj-$(CONFIG_PROC_FS)          += proc.o
> +obj-$(CONFIG_PARAVIRT)         += paravirt.o
>
>  obj-$(CONFIG_SMP)              += smp.o
>
> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> new file mode 100644
> index 000000000000..21d01d05791a
> --- /dev/null
> +++ b/arch/loongarch/kernel/paravirt.c
> @@ -0,0 +1,41 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/export.h>
> +#include <linux/types.h>
> +#include <linux/jump_label.h>
> +#include <linux/kvm_para.h>
> +#include <asm/paravirt.h>
> +#include <linux/static_call.h>
> +
> +struct static_key paravirt_steal_enabled;
> +struct static_key paravirt_steal_rq_enabled;
> +
> +static u64 native_steal_clock(int cpu)
> +{
> +       return 0;
> +}
> +
> +DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
The steal time code can be removed in this patch, I think.

> +
> +static bool kvm_para_available(void)
> +{
> +       static int hypervisor_type;
> +       int config;
> +
> +       if (!hypervisor_type) {
> +               config = read_cpucfg(CPUCFG_KVM_SIG);
> +               if (!memcmp(&config, KVM_SIGNATURE, 4))
> +                       hypervisor_type = HYPERVISOR_KVM;
> +       }
> +
> +       return hypervisor_type == HYPERVISOR_KVM;
> +}
> +
> +int __init pv_guest_init(void)
> +{
> +       if (!cpu_has_hypervisor)
> +               return 0;
> +       if (!kvm_para_available())
> +               return 0;
> +
> +       return 1;
> +}
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index edf2bba80130..de5c36dccc49 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -43,6 +43,7 @@
>  #include <asm/efi.h>
>  #include <asm/loongson.h>
>  #include <asm/numa.h>
> +#include <asm/paravirt.h>
>  #include <asm/pgalloc.h>
>  #include <asm/sections.h>
>  #include <asm/setup.h>
> @@ -367,6 +368,7 @@ void __init platform_init(void)
>         pr_info("The BIOS Version: %s\n", b_info.bios_version);
>
>         efi_runtime_init();
> +       pv_guest_init();
I prefer use CONFIG_PARAVIRT here, though you have a dummy version for
!CONFIG_PARAVIRT, I think it is better to let others clearly know that
PARAVIRT is an optional feature.

Huacai


Huacai
>  }
>
>  static void __init check_kernel_sections_mem(void)
> --
> 2.39.3
>
>