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AJvYcCUrrHgVi2+UNLFaUJIcRfAOkEW0C6W22IsY/DJPDzrjwIy6hS8rgMdpyy/3KehLokw6YKc=@vger.kernel.org X-Gm-Message-State: AOJu0YzkZITKSFhwOvOTQibJyAGmWozGfOLWH3Kyr9pLfwUJH7Tztwuk qfEosT2KkpPe+iiGFEfuf4FAERuuIHlX+qDCeF9nbZhgIPd6fUied3PTyOtdF7w2yI2j3sqCaYG hVenxZQ== X-Google-Smtp-Source: AGHT+IHHjTqKCVgw6SgsPYwqUOioEQpweKo/z/+paeQ7pN85Ant9Y+niIgm2LIEStVcV5YpSdV1Mjgyvn/A= X-Received: from plbkf5.prod.google.com ([2002:a17:903:5c5:b0:269:b2a5:8823]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:f985:b0:270:4964:ad7c with SMTP id d9443c01a7336-27cc28bc31cmr31931065ad.2.1758644126442; Tue, 23 Sep 2025 09:15:26 -0700 (PDT) Date: Tue, 23 Sep 2025 09:15:24 -0700 In-Reply-To: <287c2195-740c-4f2e-a545-c886962fc542@intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250919223258.1604852-1-seanjc@google.com> <20250919223258.1604852-19-seanjc@google.com> <287c2195-740c-4f2e-a545-c886962fc542@intel.com> Message-ID: Subject: Re: [PATCH v16 18/51] KVM: x86: Don't emulate instructions affected by CET features From: Sean Christopherson To: Xiaoyao Li Cc: Chao Gao , Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Tom Lendacky , Mathias Krause , John Allen , Rick Edgecombe , Binbin Wu , Maxim Levitsky , Zhang Yi Z , Xin Li Content-Type: text/plain; charset="us-ascii" On Tue, Sep 23, 2025, Xiaoyao Li wrote: > On 9/23/2025 4:04 AM, Sean Christopherson wrote: > Two nits besides, > > Link:https://lore.kernel.org/r/20250919223258.1604852-19-seanjc@google.com > > Signed-off-by: Sean Christopherson > > --- > > arch/x86/kvm/emulate.c | 117 ++++++++++++++++++++++++++++++++++++----- > > 1 file changed, 103 insertions(+), 14 deletions(-) > > > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > > index 23929151a5b8..a7683dc18405 100644 > > --- a/arch/x86/kvm/emulate.c > > +++ b/arch/x86/kvm/emulate.c > > @@ -178,6 +178,7 @@ > > #define IncSP ((u64)1 << 54) /* SP is incremented before ModRM calc */ > > #define TwoMemOp ((u64)1 << 55) /* Instruction has two memory operand */ > > #define IsBranch ((u64)1 << 56) /* Instruction is considered a branch. */ > > +#define ShadowStack ((u64)1 << 57) /* Instruction affects Shadow Stacks. */ > > #define DstXacc (DstAccLo | SrcAccHi | SrcWrite) > > @@ -4068,9 +4069,9 @@ static const struct opcode group4[] = { > > static const struct opcode group5[] = { > > F(DstMem | SrcNone | Lock, em_inc), > > F(DstMem | SrcNone | Lock, em_dec), > > - I(SrcMem | NearBranch | IsBranch, em_call_near_abs), > > - I(SrcMemFAddr | ImplicitOps | IsBranch, em_call_far), > > - I(SrcMem | NearBranch | IsBranch, em_jmp_abs), > > + I(SrcMem | NearBranch | IsBranch | ShadowStack, em_call_near_abs), > > + I(SrcMemFAddr | ImplicitOps | IsBranch | ShadowStack, em_call_far), > > + I(SrcMem | NearBranch | IsBranch, em_jmp_abs), > > The change of this line is unexpected, since it only changes the indentation > of 'em_jmp_abs' > > static unsigned imm_size(struct x86_emulate_ctxt *ctxt) > > { > > unsigned size; > > @@ -4943,6 +4998,40 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len, int > > ctxt->execute = opcode.u.execute; > > + /* > > + * Reject emulation if KVM might need to emulate shadow stack updates > > + * and/or indirect branch tracking enforcement, which the emulator > > + * doesn't support. > > + */ > > + if ((is_ibt_instruction(ctxt) || is_shstk_instruction(ctxt)) && > > + ctxt->ops->get_cr(ctxt, 4) & X86_CR4_CET) { > > + u64 u_cet = 0, s_cet = 0; > > + > > + /* > > + * Check both User and Supervisor on far transfers as inter- > > + * privilege level transfers are impacted by CET at the target > > + * privilege level, and that is not known at this time. The > > + * the expectation is that the guest will not require emulation > > Dobule 'the' Squashed fixes for both, thanks!