On Fri, Nov 04, 2022, Paolo Bonzini wrote:
> On 11/3/22 19:58, Sean Christopherson wrote:
> >
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index 3e508f239098..ebe617ab0b37 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -191,6 +191,8 @@ static void default_init(struct cpuinfo_x86 *c)
> > strcpy(c->x86_model_id, "386");
> > }
> > #endif
> > +
> > + clear_cpu_cap(c, X86_FEATURE_MSR_IA32_FEAT_CTL);
> > }
> > static const struct cpu_dev default_cpu = {
>
> Not needed I think? default_init does not call init_ia32_feat_ctl.
cpuid_deps is only processed by do_clear_cpu_cap(), so unless there's an explicit
"clear" action, the dependencies will not be updated. It kinda makes sense since
hardware-based features shouldn't end up with scenarios where a dependent feature
exists but the base feature does not (barring bad KVM setups :-) ).
That said, this seems like a bug waiting to happen, and unless I'm missing something
it's quite straightforward to process all dependencies during setup. Time to find
out if Boris and co. agree :-)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 1a85e1fb0922..c4408d03b180 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -147,6 +147,7 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
extern void setup_clear_cpu_cap(unsigned int bit);
extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
+extern void apply_cpuid_deps(struct cpuinfo_x86 *c);
#define setup_force_cpu_cap(bit) do { \
set_cpu_cap(&boot_cpu_data, bit); \
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3e508f239098..28ce31dadd7f 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1884,6 +1884,8 @@ static void identify_cpu(struct cpuinfo_x86 *c)
c->x86_capability[i] |= boot_cpu_data.x86_capability[i];
}
+ apply_cpuid_deps(c);
+
ppin_init(c);
/* Init Machine Check Exception if available. */
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index c881bcafba7d..7e91e97973ca 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -138,3 +138,13 @@ void setup_clear_cpu_cap(unsigned int feature)
{
do_clear_cpu_cap(NULL, feature);
}
+
+void apply_cpuid_deps(struct cpuinfo_x86 *c)
+{
+ const struct cpuid_dep *d;
+
+ for (d = cpuid_deps; d->feature; d++) {
+ if (!cpu_has(c, d->feature))
+ clear_cpu_cap(c, d->feature);
+ }
+}
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