linux-kernel - [V3 PATCH 4/4] KVM: selftests: x86: Precompute the cpu type

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Date:   Thu, 13 Oct 2022 12:13:19 +0000
From:   Vishal Annapurve <vannapurve@...gle.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     pbonzini@...hat.com, shuah@...nel.org, bgardon@...gle.com,
        seanjc@...gle.com, oupton@...gle.com, peterx@...hat.com,
        vkuznets@...hat.com, dmatlack@...gle.com,
        Vishal Annapurve <vannapurve@...gle.com>
Subject: [V3 PATCH 4/4] KVM: selftests: x86: Precompute the cpu type

Cache the vendor CPU type in a global variable so that multiple calls
to is_amd/intel_cpu() do not need to re-execute CPUID.

Sync the global variable is_cpu_amd into the guest so the guest can also
avoid executing CPUID instruction.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Vishal Annapurve <vannapurve@...gle.com>
---
 tools/testing/selftests/kvm/lib/x86_64/processor.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index fa65e8142c16..f508e58346e9 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)
 {
@@ -1046,7 +1047,7 @@ static bool cpu_vendor_string_is(const char *vendor)
 
 bool is_intel_cpu(void)
 {
-	return cpu_vendor_string_is("GenuineIntel");
+	return !is_cpu_amd;
 }
 
 /*
@@ -1054,7 +1055,7 @@ bool is_intel_cpu(void)
  */
 bool is_amd_cpu(void)
 {
-	return cpu_vendor_string_is("AuthenticAMD");
+	return is_cpu_amd;
 }
 
 void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits)
@@ -1328,8 +1329,13 @@ bool vm_is_unrestricted_guest(struct kvm_vm *vm)
 	return get_kvm_intel_param_bool("unrestricted_guest");
 }
 
+void kvm_selftest_arch_init(void)
+{
+	is_cpu_amd = cpu_vendor_string_is("AuthenticAMD");
+}
 
 void kvm_arch_vm_post_create(struct kvm_vm *vm)
 {
 	vm_create_irqchip(vm);
+	sync_global_to_guest(vm, is_cpu_amd);
 }
-- 
2.38.0.rc1.362.ged0d419d3c-goog