On Fri, Jun 14, 2019 at 03:41:23PM +0200, Borislav Petkov wrote:
> + Radim and Paolo. See upthread for context.
>
> On Fri, Jun 14, 2019 at 06:17:02AM -0700, Fenghua Yu wrote:
> > > Alternatively - and what I think is the better solution - would be to
> > > remove those BUILD_BUG_ONs in x86_feature_cpuid and filter out the
> > > Linux-defined leafs dynamically. This way the array won't have holes in
> > > it.
> >
> > Maybe adding a dummy slot in cpuid_leafs in patch 0002 to avoid the
> > compilation errors?
>
> Maybe you didn't read what you're replying to: "This way the array
> won't have holes in it". Ontop of yours:
>
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index d78a61408243..03d6f3f7b27c 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -47,6 +47,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
> [CPUID_8000_0001_ECX] = {0x80000001, 0, CPUID_ECX},
> [CPUID_7_0_EBX] = { 7, 0, CPUID_EBX},
> [CPUID_D_1_EAX] = { 0xd, 1, CPUID_EAX},
> + [CPUID_7_1_EAX] = { 7, 1, CPUID_EAX},
> [CPUID_8000_0008_EBX] = {0x80000008, 0, CPUID_EBX},
> [CPUID_6_EAX] = { 6, 0, CPUID_EAX},
> [CPUID_8000_000A_EDX] = {0x8000000a, 0, CPUID_EDX},
> @@ -59,8 +60,9 @@ static __always_inline struct cpuid_reg
> x86_feature_cpuid(unsigned x86_feature)
> {
> unsigned x86_leaf = x86_feature / 32;
>
> - BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid));
> - BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
> + if (x86_leaf == CPUID_LNX_1 ||
> + x86_leaf == CPUID_LNX_4)
> + return NULL;
>
> return reverse_cpuid[x86_leaf];
> }
>
> That's what I mean with filter out dynamically.
This is wrong. KVM isn't complaining about shuffling the order of feature
words, it's complaining that code is trying to do a reverse CPUID lookup
to a feature that isn't in the reverse_cpuid table. Filtering out
checks dynamically is just hiding bugs.
>In function ‘x86_feature_cpuid’,
> inlined from ‘guest_cpuid_get_register’ at arch/x86/kvm/cpuid.h:71:33,
> inlined from ‘guest_cpuid_has’ at arch/x86/kvm/cpuid.h:100:8,
> inlined from ‘kvm_get_msr_common’ at arch/x86/kvm/x86.c:2804:8:
This corresponds to "guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES)",
i.e. KVM is trying to query X86_FEATURE_ARCH_CAPABILITIES and is yelling
that there is no reverse_cpuid entry for CPUID_7_EDX.
The problem is that 'enum cpuid_leafs' no longer matches up with the
word numbers defined in cpufeatures.h, e.g. CPUID_7_EDX == 17 or so, but
the entries in cpufeatures.h defined CPUID_7_EDX flags using word 18.
This patch also needs to modify NCAPINTS.
