Messages in this thread | | | Subject | Re: [PATCH 1/6] KVM: x86: Fix tracing of CPUID.function when function is out-of-range | From | Xiaoyao Li <> | Date | Tue, 3 Mar 2020 10:27:47 +0800 |
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On 3/3/2020 4:49 AM, Sean Christopherson wrote: > On Mon, Mar 02, 2020 at 09:26:54PM +0100, Jan Kiszka wrote: >> On 02.03.20 20:57, Sean Christopherson wrote: >>> Rework kvm_cpuid() to query entry->function when adjusting the output >>> values so that the original function (in the aptly named "function") is >>> preserved for tracing. This fixes a bug where trace_kvm_cpuid() will >>> trace the max function for a range instead of the requested function if >>> the requested function is out-of-range and an entry for the max function >>> exists. >>> >>> Fixes: 43561123ab37 ("kvm: x86: Improve emulation of CPUID leaves 0BH and 1FH") >>> Reported-by: Jan Kiszka <jan.kiszka@siemens.com> >>> Cc: Jim Mattson <jmattson@google.com> >>> Cc: Xiaoyao Li <xiaoyao.li@intel.com> >>> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> >>> --- >>> arch/x86/kvm/cpuid.c | 15 +++++++-------- >>> 1 file changed, 7 insertions(+), 8 deletions(-) >>> >>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c >>> index b1c469446b07..6be012937eba 100644 >>> --- a/arch/x86/kvm/cpuid.c >>> +++ b/arch/x86/kvm/cpuid.c >>> @@ -997,12 +997,12 @@ static bool cpuid_function_in_range(struct kvm_vcpu *vcpu, u32 function) >>> return max && function <= max->eax; >>> } >>> +/* Returns true if the requested leaf/function exists in guest CPUID. */ >>> bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, >>> u32 *ecx, u32 *edx, bool check_limit) >>> { >>> - u32 function = *eax, index = *ecx; >>> + const u32 function = *eax, index = *ecx; >>> struct kvm_cpuid_entry2 *entry; >>> - struct kvm_cpuid_entry2 *max; >>> bool found; >>> entry = kvm_find_cpuid_entry(vcpu, function, index); >>> @@ -1015,18 +1015,17 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, >>> */ >>> if (!entry && check_limit && !guest_cpuid_is_amd(vcpu) && >>> !cpuid_function_in_range(vcpu, function)) { >>> - max = kvm_find_cpuid_entry(vcpu, 0, 0); >>> - if (max) { >>> - function = max->eax; >>> - entry = kvm_find_cpuid_entry(vcpu, function, index); >>> - } >>> + entry = kvm_find_cpuid_entry(vcpu, 0, 0); >>> + if (entry) >>> + entry = kvm_find_cpuid_entry(vcpu, entry->eax, index); >>> } >>> if (entry) { >>> *eax = entry->eax; >>> *ebx = entry->ebx; >>> *ecx = entry->ecx; >>> *edx = entry->edx; >>> - if (function == 7 && index == 0) { >>> + >>> + if (entry->function == 7 && index == 0) { >>> u64 data; >>> if (!__kvm_get_msr(vcpu, MSR_IA32_TSX_CTRL, &data, true) && >>> (data & TSX_CTRL_CPUID_CLEAR)) >>> >> >> What about the !entry case below this? It was impacted by the function >> capping so far, not it's no longer. > > Hmm, the only way the output would be different is in a really contrived > scenario where userspace doesn't provide an entry for the max basic leaf. > > The !entry path can only be reached with "orig_function != function" if > orig_function is out of range and there is no entry for the max basic leaf.
> The adjustments for 0xb/0x1f require the max basic leaf to be 0xb or 0x1f, > and to take effect with !entry would require there to be a CPUID.max.1 but > not a CPUID.max.0. That'd be a violation of Intel's SDM, i.e. it's bogus > userspace input and IMO can be ignored. >
Sorry I cannot catch you. Why it's a violation of Intel's SDM?
Supposing the max basic is 0x1f, and it queries cpuid(0x20, 0x5), it should return cpuid(0x1f, 0x5).
But based on this patch, it returns all zeros.
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