From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH] KVM: svm: add support for RDTSCP Date: Thu, 12 Nov 2015 15:45:09 +0100 Message-ID: <20151112144509.GD13027@8bytes.org> References: <1447336157-3122-1-git-send-email-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <1447336157-3122-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Hi Paolo, On Thu, Nov 12, 2015 at 02:49:16PM +0100, Paolo Bonzini wrote: > RDTSCP was never supported for AMD CPUs, which nobody noticed because > Linux does not use it. But exactly the fact that Linux does not > use it makes the implementation very simple; we can freely trash > MSR_TSC_AUX while running the guest. > > Cc: Joerg Roedel > Signed-off-by: Paolo Bonzini > --- > arch/x86/kvm/svm.c | 24 +++++++++++++++++++++++- > 1 file changed, 23 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index 83a1c64..c302614 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -86,6 +86,7 @@ static const u32 host_save_user_msrs[] = { > MSR_FS_BASE, > #endif > MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP, > + MSR_TSC_AUX, > }; > > #define NR_HOST_SAVE_USER_MSRS ARRAY_SIZE(host_save_user_msrs) > @@ -135,6 +136,7 @@ struct vcpu_svm { > uint64_t asid_generation; > uint64_t sysenter_esp; > uint64_t sysenter_eip; > + uint64_t tsc_aux; > > u64 next_rip; > > @@ -1238,6 +1240,9 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > wrmsrl(MSR_AMD64_TSC_RATIO, tsc_ratio); > } > } > + /* This assumes that the kernel never uses MSR_TSC_AUX */ > + if (static_cpu_has(X86_FEATURE_RDTSCP)) > + wrmsrl(MSR_TSC_AUX, svm->tsc_aux); > } Hmm, you seem to still intercept MSR_TSC_AUX, is that intentional? Loading the guests value into the real cpu msr only makes sense to me when the MSR is no longer intercepted. Joerg