From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Joerg Roedel" <joro@8bytes.org>,
"Jim Mattson" <jmattson@google.com>
Subject: Re: [PATCH v3 5/7] x86: KVM: svm: remove hardcoded instruction length from intercepts
Date: Fri, 9 Aug 2019 11:37:30 -0700 [thread overview]
Message-ID: <20190809183730.GE10541@linux.intel.com> (raw)
In-Reply-To: <20190808173051.6359-6-vkuznets@redhat.com>
On Thu, Aug 08, 2019 at 07:30:49PM +0200, Vitaly Kuznetsov wrote:
> Various intercepts hard-code the respective instruction lengths to optimize
> skip_emulated_instruction(): when next_rip is pre-set we skip
> kvm_emulate_instruction(vcpu, EMULTYPE_SKIP). The optimization is, however,
> incorrect: different (redundant) prefixes could be used to enlarge the
> instruction. We can't really avoid decoding.
>
> svm->next_rip is not used when CPU supports 'nrips' (X86_FEATURE_NRIPS)
> feature: next RIP is provided in VMCB. The feature is not really new
> (Opteron G3s had it already) and the change should have zero affect.
>
> Remove manual svm->next_rip setting with hard-coded instruction lengths.
> The only case where we now use svm->next_rip is EXIT_IOIO: the instruction
> length is provided to us by hardware.
>
> Hardcoded RIP advancement remains in vmrun_interception(), this is going to
> be taken care of separately.
>
> Reported-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
next prev parent reply other threads:[~2019-08-09 18:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-08 17:30 [PATCH v3 0/7] x86: KVM: svm: get rid of hardcoded instructions lengths Vitaly Kuznetsov
2019-08-08 17:30 ` [PATCH v3 1/7] x86: KVM: svm: don't pretend to advance RIP in case wrmsr_interception() results in #GP Vitaly Kuznetsov
2019-08-08 17:30 ` [PATCH v3 2/7] x86: kvm: svm: propagate errors from skip_emulated_instruction() Vitaly Kuznetsov
2019-08-09 18:31 ` Sean Christopherson
2019-08-08 17:30 ` [PATCH v3 3/7] x86: KVM: clear interrupt shadow on EMULTYPE_SKIP Vitaly Kuznetsov
2019-08-08 17:30 ` [PATCH v3 4/7] x86: KVM: add xsetbv to the emulator Vitaly Kuznetsov
2019-08-08 17:30 ` [PATCH v3 5/7] x86: KVM: svm: remove hardcoded instruction length from intercepts Vitaly Kuznetsov
2019-08-09 18:37 ` Sean Christopherson [this message]
2019-08-08 17:30 ` [PATCH v3 6/7] x86: KVM: svm: eliminate weird goto from vmrun_interception() Vitaly Kuznetsov
2019-08-09 18:46 ` Sean Christopherson
2019-08-08 17:30 ` [PATCH v3 7/7] x86: KVM: svm: eliminate hardcoded RIP advancement " Vitaly Kuznetsov
2019-08-09 18:55 ` Sean Christopherson
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