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[91.219.240.8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42f8599487fsm14464875e9.0.2024.10.04.02.02.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Oct 2024 02:02:35 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson , Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 04/11] KVM: selftests: Rework OSXSAVE CR4=>CPUID test to play nice with AVX insns In-Reply-To: <20241003234337.273364-5-seanjc@google.com> References: <20241003234337.273364-1-seanjc@google.com> <20241003234337.273364-5-seanjc@google.com> Date: Fri, 04 Oct 2024 11:02:34 +0200 Message-ID: <87r08wi6l1.fsf@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Sean Christopherson writes: > Rework the CR4/CPUID sync test to clear CR4.OSXSAVE, do CPUID, and restore > CR4.OSXSAVE in assembly, so that there is zero chance of AVX instructions > being executed while CR4.OSXSAVE is disabled. This will allow enabling > CR4.OSXSAVE by default for selftests vCPUs as a general means of playing > nice with AVX instructions. > > Signed-off-by: Sean Christopherson > --- > .../kvm/x86_64/cr4_cpuid_sync_test.c | 46 +++++++++++++------ > 1 file changed, 32 insertions(+), 14 deletions(-) > > diff --git a/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c b/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c > index 624dc725e14d..da818afb7031 100644 > --- a/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c > +++ b/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c > @@ -19,15 +19,14 @@ > #include "kvm_util.h" > #include "processor.h" > > -static inline bool cr4_cpuid_is_sync(void) > -{ > - uint64_t cr4 = get_cr4(); > - > - return (this_cpu_has(X86_FEATURE_OSXSAVE) == !!(cr4 & X86_CR4_OSXSAVE)); > -} > +#define MAGIC_HYPERCALL_PORT 0x80 > > static void guest_code(void) > { > + u32 regs[4] = { > + [KVM_CPUID_EAX] = X86_FEATURE_OSXSAVE.function, > + [KVM_CPUID_ECX] = X86_FEATURE_OSXSAVE.index, > + }; > uint64_t cr4; > > /* turn on CR4.OSXSAVE */ > @@ -36,13 +35,29 @@ static void guest_code(void) > set_cr4(cr4); > > /* verify CR4.OSXSAVE == CPUID.OSXSAVE */ > - GUEST_ASSERT(cr4_cpuid_is_sync()); > + GUEST_ASSERT(this_cpu_has(X86_FEATURE_OSXSAVE)); > > - /* notify hypervisor to change CR4 */ > - GUEST_SYNC(0); > + /* > + * Notify hypervisor to clear CR4.0SXSAVE, do CPUID and save output, > + * and then restore CR4. Do this all in assembly to ensure no AVX > + * instructions are executed while OSXSAVE=0. > + */ > + asm volatile ( > + "out %%al, $" __stringify(MAGIC_HYPERCALL_PORT) "\n\t" > + "cpuid\n\t" > + "mov %%rdi, %%cr4\n\t" > + : "+a" (regs[KVM_CPUID_EAX]), > + "=b" (regs[KVM_CPUID_EBX]), > + "+c" (regs[KVM_CPUID_ECX]), > + "=d" (regs[KVM_CPUID_EDX]) > + : "D" (get_cr4()) > + ); > > - /* check again */ > - GUEST_ASSERT(cr4_cpuid_is_sync()); > + /* Verify KVM cleared OSXSAVE in CPUID when it was cleared in CR4. */ > + GUEST_ASSERT(!(regs[X86_FEATURE_OSXSAVE.reg] & BIT(X86_FEATURE_OSXSAVE.bit))); > + > + /* Verify restoring CR4 also restored OSXSAVE in CPUID. */ > + GUEST_ASSERT(this_cpu_has(X86_FEATURE_OSXSAVE)); > > GUEST_DONE(); > } > @@ -62,13 +77,16 @@ int main(int argc, char *argv[]) > vcpu_run(vcpu); > TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO); > > - switch (get_ucall(vcpu, &uc)) { > - case UCALL_SYNC: > + if (vcpu->run->io.port == MAGIC_HYPERCALL_PORT && > + vcpu->run->io.direction == KVM_EXIT_IO_OUT) { > /* emulate hypervisor clearing CR4.OSXSAVE */ > vcpu_sregs_get(vcpu, &sregs); > sregs.cr4 &= ~X86_CR4_OSXSAVE; > vcpu_sregs_set(vcpu, &sregs); > - break; > + continue; > + } > + > + switch (get_ucall(vcpu, &uc)) { > case UCALL_ABORT: > REPORT_GUEST_ASSERT(uc); > break; Reviewed-by: Vitaly Kuznetsov -- Vitaly