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@google.com Signed-off-by: Vishal Annapurve vannapurve@google.com
.../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