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[34.125.103.223]) by smtp.gmail.com with ESMTPSA id k17-20020a170902c41100b001750361f430sm2520669plk.155.2022.09.21.14.19.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Sep 2022 14:19:06 -0700 (PDT) Date: Wed, 21 Sep 2022 14:19:02 -0700 From: David Matlack To: Vishal Annapurve Cc: x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, pbonzini@redhat.com, shuah@kernel.org, bgardon@google.com, seanjc@google.com, oupton@google.com, peterx@redhat.com, vkuznets@redhat.com Subject: Re: [V2 PATCH 4/8] KVM: selftests: x86: Precompute the result for is_{intel,amd}_cpu() Message-ID: References: <20220915000448.1674802-1-vannapurve@google.com> <20220915000448.1674802-5-vannapurve@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220915000448.1674802-5-vannapurve@google.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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 > Signed-off-by: Vishal Annapurve > --- > .../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 >