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    SubjectRe: [PATCH RFC 1/2] KVM: x86: generalize guest_cpuid_has_ helpers
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    On 02/08/2017 22:41, Radim Krčmář wrote:
    > This patch turns guest_cpuid_has_XYZ(cpuid) into guest_cpuid_has(cpuid,
    > X86_FEATURE_XYZ), which gets rid of many very similar helpers.
    >
    > When seeing a X86_FEATURE_*, we can know which cpuid it belongs to, but
    > this information isn't in common code, so we recreate it for KVM.
    >
    > Add some BUILD_BUG_ONs to make sure that it runs nicely.
    >
    > Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
    > ---
    > arch/x86/kvm/cpuid.h | 202 +++++++++++++++++----------------------------------
    > arch/x86/kvm/mmu.c | 7 +-
    > arch/x86/kvm/mtrr.c | 2 +-
    > arch/x86/kvm/svm.c | 2 +-
    > arch/x86/kvm/vmx.c | 26 +++----
    > arch/x86/kvm/x86.c | 38 +++++-----
    > 6 files changed, 105 insertions(+), 172 deletions(-)
    >
    > diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
    > index da6728383052..3b17d915b608 100644
    > --- a/arch/x86/kvm/cpuid.h
    > +++ b/arch/x86/kvm/cpuid.h
    > @@ -3,6 +3,7 @@
    >
    > #include "x86.h"
    > #include <asm/cpu.h>
    > +#include <asm/processor.h>
    >
    > int kvm_update_cpuid(struct kvm_vcpu *vcpu);
    > bool kvm_mpx_supported(void);
    > @@ -29,95 +30,78 @@ static inline int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
    > return vcpu->arch.maxphyaddr;
    > }
    >
    > -static inline bool guest_cpuid_has_xsave(struct kvm_vcpu *vcpu)
    > +struct cpuid_reg {
    > + u32 function;
    > + u32 index;
    > + int reg;
    > +};
    > +
    > +static const struct cpuid_reg reverse_cpuid[] = {
    > + [CPUID_1_EDX] = { 1, 0, CPUID_EDX},
    > + [CPUID_8000_0001_EDX] = {0x80000001, 0, CPUID_EDX},
    > + [CPUID_8086_0001_EDX] = {0x80860001, 0, CPUID_EDX},
    > + [CPUID_1_ECX] = { 1, 0, CPUID_ECX},
    > + [CPUID_C000_0001_EDX] = {0xc0000001, 0, CPUID_EDX},
    > + [CPUID_8000_0001_ECX] = {0xc0000001, 0, CPUID_ECX},
    > + [CPUID_7_0_EBX] = { 7, 0, CPUID_EBX},
    > + [CPUID_D_1_EAX] = { 0xd, 1, CPUID_EAX},
    > + [CPUID_F_0_EDX] = { 0xf, 0, CPUID_EDX},
    > + [CPUID_F_1_EDX] = { 0xf, 1, CPUID_EDX},
    > + [CPUID_8000_0008_EBX] = {0x80000008, 0, CPUID_EBX},
    > + [CPUID_6_EAX] = { 6, 0, CPUID_EAX},
    > + [CPUID_8000_000A_EDX] = {0x8000000a, 0, CPUID_EDX},
    > + [CPUID_7_ECX] = { 7, 0, CPUID_ECX},
    > + [CPUID_8000_0007_EBX] = {0x80000007, 0, CPUID_EBX},
    > +};
    > +
    > +static inline struct cpuid_reg x86_feature_cpuid(unsigned x86_feature)
    > +{
    > + unsigned x86_leaf = x86_feature / 32;
    > +
    > + BUILD_BUG_ON(!__builtin_constant_p(x86_leaf));
    > + BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid));
    > + BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
    > +
    > + return reverse_cpuid[x86_leaf];
    > +}
    > +
    > +static inline int *guest_cpuid_get_register(struct kvm_vcpu *vcpu, unsigned x86_feature)
    > {
    > struct kvm_cpuid_entry2 *best;
    > + struct cpuid_reg cpuid = x86_feature_cpuid(x86_feature);
    >
    > - if (!static_cpu_has(X86_FEATURE_XSAVE))
    > + best = kvm_find_cpuid_entry(vcpu, cpuid.function, cpuid.index);
    > + if (!best)
    > + return NULL;
    > +
    > + switch (cpuid.reg) {
    > + case CPUID_EAX:
    > + return &best->eax;
    > + case CPUID_EBX:
    > + return &best->ebx;
    > + case CPUID_ECX:
    > + return &best->ecx;
    > + case CPUID_EDX:
    > + return &best->edx;
    > + default:
    > + BUILD_BUG();
    > + return NULL;
    > + }
    > +}

    Wow, I didn't expect the compiler to be able to inline all of this and
    even do BUILD_BUG_ON()s on array lookups. Maybe change inline to
    __always_inline just to be safe?

    If anybody complains we can make it just a BUG.

    Paolo

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