From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 497CE75801; Mon, 4 May 2026 14:03:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777903388; cv=none; b=MuMVs2xSaLnnY0uyWmXB0A/CMT9x3a8pWUbsysQ6b9qrexwJ264lr4LgdVFrAy8MEZqdITcMLdmAbAWQ0Clki1yD6yR+nabwg0TlndfjE93ryuXy5fpESe4PSOpYtQj50A+rAzgPqgd+hpydQQppw/SH2+adKsO91UvugMghNPI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777903388; c=relaxed/simple; bh=tR7S/vg5O6L9N/dLvu+YCTCKQImWYHdWzCCF/CJL3OU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VHwtDgIfjh9gRe4VYn44jj0KtFad+yEKm/IXEHf1Sc5q1wNxitEqTD8F2NY2Mi98dtZfJILpfDdLY0xjjsUHmON4LIdakeUQZszLkGyVUQ5p3MB4TI9imUFhvt0tk6xM2E9shyo/7v4mt6E4vdwZxv4IBQF1VglW7L+OnmquyMY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=LBEIAeoc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="LBEIAeoc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 90474C2BCB8; Mon, 4 May 2026 14:03:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777903387; bh=tR7S/vg5O6L9N/dLvu+YCTCKQImWYHdWzCCF/CJL3OU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LBEIAeocI2UTkC99nNtc1N2iUG2tvbBr3vfWns4O+RhU1gci93LWG4mwV5st7PfWo so0Gx6RsJ1u7th1mfu8UZ4srxXJtZR2BdBpoi+0pKp+XXUdG2krz5vgwuqqyeBBvh2 YxNmT6/3hnXVtEcREiA2L16C5gpNgtF3zbETYyNw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jim Mattson , Yosry Ahmed , Sean Christopherson Subject: [PATCH 7.0 215/307] KVM: SVM: Add missing save/restore handling of LBR MSRs Date: Mon, 4 May 2026 15:51:40 +0200 Message-ID: <20260504135150.957179987@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260504135142.814938198@linuxfoundation.org> References: <20260504135142.814938198@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yosry Ahmed commit 3700f0788da6acf73b2df56690f4b201aa4aefd2 upstream. MSR_IA32_DEBUGCTLMSR and LBR MSRs are currently not enumerated by KVM_GET_MSR_INDEX_LIST, and LBR MSRs cannot be set with KVM_SET_MSRS. So save/restore is completely broken. Fix it by adding the MSRs to msrs_to_save_base, and allowing writes to LBR MSRs from userspace only (as they are read-only MSRs) if LBR virtualization is enabled. Additionally, to correctly restore L1's LBRs while L2 is running, make sure the LBRs are copied from the captured VMCB01 save area in svm_copy_vmrun_state(). Note, for VMX, this also fixes a flaw where MSR_IA32_DEBUGCTLMSR isn't reported as an MSR to save/restore. Note #2, over-reporting MSR_IA32_LASTxxx on Intel is ok, as KVM already handles unsupported reads and writes thanks to commit b5e2fec0ebc3 ("KVM: Ignore DEBUGCTL MSRs with no effect") (kvm_do_msr_access() will morph the unsupported userspace write into a nop). Fixes: 24e09cbf480a ("KVM: SVM: enable LBR virtualization") Cc: stable@vger.kernel.org Reported-by: Jim Mattson Signed-off-by: Yosry Ahmed Link: https://patch.msgid.link/20260303003421.2185681-4-yosry@kernel.org [sean: guard with lbrv checks, massage changelog] Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/nested.c | 5 +++++ arch/x86/kvm/svm/svm.c | 42 +++++++++++++++++++++++++++++++++++++----- arch/x86/kvm/x86.c | 3 +++ 3 files changed, 45 insertions(+), 5 deletions(-) --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -1109,6 +1109,11 @@ void svm_copy_vmrun_state(struct vmcb_sa to_save->isst_addr = from_save->isst_addr; to_save->ssp = from_save->ssp; } + + if (kvm_cpu_cap_has(X86_FEATURE_LBRV)) { + svm_copy_lbrs(to_save, from_save); + to_save->dbgctl &= ~DEBUGCTL_RESERVED_BITS; + } } void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb) --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -2788,19 +2788,19 @@ static int svm_get_msr(struct kvm_vcpu * msr_info->data = svm->tsc_aux; break; case MSR_IA32_DEBUGCTLMSR: - msr_info->data = svm->vmcb->save.dbgctl; + msr_info->data = lbrv ? svm->vmcb->save.dbgctl : 0; break; case MSR_IA32_LASTBRANCHFROMIP: - msr_info->data = svm->vmcb->save.br_from; + msr_info->data = lbrv ? svm->vmcb->save.br_from : 0; break; case MSR_IA32_LASTBRANCHTOIP: - msr_info->data = svm->vmcb->save.br_to; + msr_info->data = lbrv ? svm->vmcb->save.br_to : 0; break; case MSR_IA32_LASTINTFROMIP: - msr_info->data = svm->vmcb->save.last_excp_from; + msr_info->data = lbrv ? svm->vmcb->save.last_excp_from : 0; break; case MSR_IA32_LASTINTTOIP: - msr_info->data = svm->vmcb->save.last_excp_to; + msr_info->data = lbrv ? svm->vmcb->save.last_excp_to : 0; break; case MSR_VM_HSAVE_PA: msr_info->data = svm->nested.hsave_msr; @@ -3075,6 +3075,38 @@ static int svm_set_msr(struct kvm_vcpu * vmcb_mark_dirty(svm->vmcb, VMCB_LBR); svm_update_lbrv(vcpu); break; + case MSR_IA32_LASTBRANCHFROMIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.br_from = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; + case MSR_IA32_LASTBRANCHTOIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.br_to = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; + case MSR_IA32_LASTINTFROMIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.last_excp_from = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; + case MSR_IA32_LASTINTTOIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.last_excp_to = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; case MSR_VM_HSAVE_PA: /* * Old kernels did not validate the value written to --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -351,6 +351,9 @@ static const u32 msrs_to_save_base[] = { MSR_IA32_U_CET, MSR_IA32_S_CET, MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP, MSR_IA32_PL2_SSP, MSR_IA32_PL3_SSP, MSR_IA32_INT_SSP_TAB, + MSR_IA32_DEBUGCTLMSR, + MSR_IA32_LASTBRANCHFROMIP, MSR_IA32_LASTBRANCHTOIP, + MSR_IA32_LASTINTFROMIP, MSR_IA32_LASTINTTOIP, }; static const u32 msrs_to_save_pmu[] = {