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Mon, 06 Jul 2026 15:10:14 -0700 (PDT) Message-ID: <0e576fd8d8cd2ed1739cee36eba393fea7745506.camel@redhat.com> Subject: Re: [PATCH 0/2] KVM: nSVM: Expose DecodeAssists to L1 From: mlevitsk@redhat.com To: Jim Mattson , Tina Zhang Cc: Sean Christopherson , Paolo Bonzini , kvm@vger.kernel.org, Shuah Khan , zhouyanjing@hygon.cn, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 06 Jul 2026 18:10:12 -0400 In-Reply-To: References: <20260629125205.52394-1-zhang_wei@open-hieco.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 (3.52.4-2.fc40) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-06-30 at 08:52 -0700, Jim Mattson wrote: > On Mon, Jun 29, 2026 at 5:57=E2=80=AFAM Tina Zhang wrote: > >=20 > > The SVM DecodeAssists feature is reported in CPUID > > Fn8000_000A_EDX[7].=C2=A0 When available, hardware provides the length = and bytes > > of the intercepted instruction in the VMCB, allowing a hypervisor to co= nsume > > the decode information directly instead of re-decoding the instruction = in > > software on relevant VM-Exit paths. >=20 > DecodeAssists actually comprises four components: > * GPR number in EXITINFO1 for MOV-CR and MOV-DR VM-exits > * Software interrupt number in EXITINFO1 for INTn VM-exits > * Linear address in EXITINFO1 for INVLPG[A] VM-exits > * Guest instruction bytes and length in the VMCB for #NPF and #PF VM-exit= s >=20 > You only partially address the last component. >=20 Yes, and I also remember when I implemented some of the optional SVM featur= es, I decided not to implement this, also because of the same reason - pass-thr= ough is easy but for all the emulated VM exits, it can be tricky to get that rig= ht. Best regards, Maxim Levitsky