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Message-ID: <Y2UydNBFR3e2DAe7@google.com>
Date: Fri, 4 Nov 2022 15:40:36 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
Anup Patel <anup@...infault.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Matthew Rosato <mjrosato@...ux.ibm.com>,
Eric Farman <farman@...ux.ibm.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
James Morse <james.morse@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Oliver Upton <oliver.upton@...ux.dev>,
Atish Patra <atishp@...shpatra.org>,
David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
kvmarm@...ts.cs.columbia.edu, linux-mips@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
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Isaku Yamahata <isaku.yamahata@...el.com>,
Fabiano Rosas <farosas@...ux.ibm.com>,
Michael Ellerman <mpe@...erman.id.au>,
Chao Gao <chao.gao@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Yuan Yao <yuan.yao@...el.com>
Subject: Re: [PATCH 33/44] KVM: x86: Do VMX/SVM support checks directly in
vendor code
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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