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 12:16:35 +0800 |
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On 3/3/2020 12:08 PM, Sean Christopherson wrote: > On Tue, Mar 03, 2020 at 10:50:03AM +0800, Xiaoyao Li wrote: >> On 3/3/2020 3:57 AM, 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); >> >> There is a problem. >> >> when queried leaf is out of range on Intel CPU, it returns the maximum basic >> leaf, and any dependence on input ECX (i.e., subleaf) value in the basic >> leaf is honored. As disclaimed in SDM of CPUID instruction. > > That's what the code above does. > >> The ECX should be honored if and only the leaf has a significant index. >> If the leaf doesn't has a significant index, it just ignores the EDX input > > s/EDX/ECX > >> in bare metal. >> >> So it should be something like: >> >> if (!entry && check_limit && !guest_cpuid_is_amd(vcpu) && >> !cpuid_function_in_range(vcpu, function)) { >> entry = kvm_find_cpuid_entry(vcpu, 0, 0); >> if (entry) { >> entry = kvm_find_cpuid_entry(vcpu, entry->eax, 0); >> if (entry && >> entry->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX ) { > > This is unnecessary IMO. The only scenario where SIGNFICANT_INDEX is 0 > and cpuid_entry(entry->eax, 0) != cpuid_entry(entry->eax, index) is if > userspace created a cpuid entry for index>0 with SIGNFICANT_INDEX.
I just forgot that is_matching_cpuid_entry() has taken SIGNIFICANT_INDEX into account.
Please ignore my stupid noise.
> a busted model, e.g. it'd be the SDM equivalent of an Intel CPU having > different output for CPUID.0x16.0 and CPUID.16.5 despite the SDM stating > that the CPUID.0x16 ignores the index. > > E.g. on my system with a max basic leaf of 0x16 > > $ cpuid -1 -r > CPU: > 0x00000000 0x00: eax=0x00000016 ebx=0x756e6547 ecx=0x6c65746e edx=0x49656e69 > ... > 0x00000016 0x00: eax=0x00000e74 ebx=0x0000125c ecx=0x00000064 edx=0x00000000 > > $ cpuid -1 -r -l 0x16 > CPU: > 0x00000016 0x00: eax=0x00000e74 ebx=0x0000125c ecx=0x00000064 edx=0x00000000 > ~ $ cpuid -1 -r -l 0x16 -s 4 > CPU: > 0x00000016 0x04: eax=0x00000e74 ebx=0x0000125c ecx=0x00000064 edx=0x00000000 > ~ $ cpuid -1 -r -l 0x16 -s 466 > CPU: > 0x00000016 0x1d2: eax=0x00000e74 ebx=0x0000125c ecx=0x00000064 edx=0x00000000 > > > If it returned anything else for CPUID.0x16.0x4 then it'd be a CPU bug. > Same thing here, it's a userspace bug if it creates a CPUID entry that > shouldn't exist. E.g. ignoring Intel's silly "max basic leaf" behavior > for the moment, if userspace created a entry for CPUID.0x0.N it would > break the Linux kernel's cpu_detect(), as it doesn't initialize ECX when > doing CPUID.0x0. > >> 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)) >>> >>
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