On Thu, Sep 15, 2022 at 12:04:44AM +0000, Vishal Annapurve wrote:
> Cache the vendor CPU type in a global variable so that multiple calls
> to is_intel_cpu() do not need to re-execute CPUID.
>
> Add cpu vendor check in kvm_hypercall() so that it executes correct
> vmcall/vmmcall instruction when running on Intel/AMD hosts. This avoids
> exit to KVM which anyway tries to patch the instruction according to
> the cpu type.
The commit shortlog makes no mention (nor even implies) that this commit
adds AMD support to kvm_hypercall(). Please break this commit up into 2.
One to precompute the result of is_{intel,amd}_cpu() and one to add AMD
support to kvm_hypercall().
If you really want to keep this as one commit (I don't know what the
benefit would be), please change the shortlog and commit message to
focus on the kvm_hypercall() change, as that is the real goal of this
commit. The precomputation is arguably and implementation detail. e.g.
KVM: selftest: Add support for AMD to kvm_hypercall()
Make it possible to use kvm_hypercall() on AMD by checking if running
on an AMD CPU and, if so, using vmmcall instead of vmcall. In order to
avoid executing CPUID in the guest on every call t kvm_hypercall()
(which would be slow), pre-compute the result of is_{intel,amd}_cpu()
as part of kvm_selftest_arch_init() and sync it into the guest
after loading the ELF image.
But again, it'd be cleaner just to split it up. Caching the result of
is_{intel,amd}_cpu() is useful in its own right, independent of the
kvm_hypercall() change.
>
> As part of this change, sync the global variable is_cpu_amd into the
> guest so the guest can determine which hypercall instruction to use
> without needing to re-execute CPUID for every hypercall.
>
> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
> ---
> .../testing/selftests/kvm/lib/x86_64/processor.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> index 25ae972f5c71..c0ae938772f6 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> @@ -19,6 +19,7 @@
> #define MAX_NR_CPUID_ENTRIES 100
>
> vm_vaddr_t exception_handlers;
> +static bool is_cpu_amd;
>
> static void regs_dump(FILE *stream, struct kvm_regs *regs, uint8_t indent)
> {
> @@ -1019,7 +1020,7 @@ static bool cpu_vendor_string_is(const char *vendor)
>
> bool is_intel_cpu(void)
> {
> - return cpu_vendor_string_is("GenuineIntel");
> + return (is_cpu_amd == false);
> }
>
> /*
> @@ -1027,7 +1028,7 @@ bool is_intel_cpu(void)
> */
> bool is_amd_cpu(void)
> {
> - return cpu_vendor_string_is("AuthenticAMD");
> + return (is_cpu_amd == true);
> }
>
> void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits)
> @@ -1182,9 +1183,15 @@ uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2,
> {
> uint64_t r;
>
> - asm volatile("vmcall"
> + if (is_amd_cpu())
> + asm volatile("vmmcall"
> : "=a"(r)
> : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3));
> + else
> + asm volatile("vmcall"
> + : "=a"(r)
> + : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3));
> +
> return r;
> }
>
> @@ -1314,8 +1321,10 @@ bool vm_is_unrestricted_guest(struct kvm_vm *vm)
>
> void kvm_selftest_arch_init(void)
> {
> + is_cpu_amd = cpu_vendor_string_is("AuthenticAMD");
> }
>
> void kvm_arch_post_vm_elf_load(struct kvm_vm *vm)
> {
> + sync_global_to_guest(vm, is_cpu_amd);
> }
> --
> 2.37.2.789.g6183377224-goog
>
