From: Sean Christopherson Date: Thu, 27 Feb 2025 22:24:07 +0000 (-0800) Subject: KVM: SVM: Suppress DEBUGCTL.BTF on AMD X-Git-Tag: v6.14-rc6~5^2^2~8 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d0eac42f5cecce009d315655bee341304fbe075e;p=thirdparty%2Fkernel%2Flinux.git KVM: SVM: Suppress DEBUGCTL.BTF on AMD Mark BTF as reserved in DEBUGCTL on AMD, as KVM doesn't actually support BTF, and fully enabling BTF virtualization is non-trivial due to interactions with the emulator, guest_debug, #DB interception, nested SVM, etc. Don't inject #GP if the guest attempts to set BTF, as there's no way to communicate lack of support to the guest, and instead suppress the flag and treat the WRMSR as (partially) unsupported. In short, make KVM behave the same on AMD and Intel (VMX already squashes BTF). Note, due to other bugs in KVM's handling of DEBUGCTL, the only way BTF has "worked" in any capacity is if the guest simultaneously enables LBRs. Reported-by: Ravi Bangoria Cc: stable@vger.kernel.org Reviewed-and-tested-by: Ravi Bangoria Link: https://lore.kernel.org/r/20250227222411.3490595-3-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index bdafbde1f211a..ed48465186961 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3177,6 +3177,15 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) */ data &= ~GENMASK(5, 2); + /* + * Suppress BTF as KVM doesn't virtualize BTF, but there's no + * way to communicate lack of support to the guest. + */ + if (data & DEBUGCTLMSR_BTF) { + kvm_pr_unimpl_wrmsr(vcpu, MSR_IA32_DEBUGCTLMSR, data); + data &= ~DEBUGCTLMSR_BTF; + } + if (data & DEBUGCTL_RESERVED_BITS) return 1; diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 3a931d3885e71..ea44c1da5a7c9 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -584,7 +584,7 @@ static inline bool is_vnmi_enabled(struct vcpu_svm *svm) /* svm.c */ #define MSR_INVALID 0xffffffffU -#define DEBUGCTL_RESERVED_BITS (~(DEBUGCTLMSR_BTF | DEBUGCTLMSR_LBR)) +#define DEBUGCTL_RESERVED_BITS (~DEBUGCTLMSR_LBR) extern bool dump_invalid_vmcb;