Re: [PATCH RFC 1/2] KVM: x86: generalize guest_cpuid_has_ helpers

David Hildenbrand
2017-08-04T15:21:01Z

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;

somehow I don't like the name best. entry?

> + struct cpuid_reg cpuid = x86_feature_cpuid(x86_feature);

you could make this const.

>
> - 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;
> + }
> +}
> +

[...]

> -/*
> - * NRIPS is provided through cpuidfn 0x8000000a.edx bit 3
> - */
> -#define BIT_NRIPS 3
> -
> -static inline bool guest_cpuid_has_nrips(struct kvm_vcpu *vcpu)
> -{
> - struct kvm_cpuid_entry2 *best;
> -
> - best = kvm_find_cpuid_entry(vcpu, 0x8000000a, 0);
> -
> - /*
> - * NRIPS is a scattered cpuid feature, so we can't use
> - * X86_FEATURE_NRIPS here (X86_FEATURE_NRIPS would be bit
> - * position 8, not 3).
> - */

Is it okay to ignore that comment and use X86_FEATURE_NRIPS in the
calling code?

> - return best && (best->edx & bit(BIT_NRIPS));
> -}
> -#undef BIT_NRIPS
> -
> static inline int guest_cpuid_family(struct kvm_vcpu *vcpu)
> {
> struct kvm_cpuid_entry2 *best;

> - if (index >= 0 && guest_cpuid_has_rdtscp(&vmx->vcpu))
> + if (index >= 0 && guest_cpuid_has(&vmx->vcpu, X86_FEATURE_MPX))

X86_FEATURE_RDTSCP ? (or is there an implication I don't know?)

> move_msr_up(vmx, index, save_nmsrs++);
> /*
> * MSR_STAR is only needed on long mode guests, and only

> - if (!guest_cpuid_has_rdtscp(vcpu) && !msr_info->host_initiated)
> + if (!msr_info->host_initiated &&
> + !guest_cpuid_has(vcpu, X86_FEATURE_MPX))

X86_FEATURE_RDTSCP ?

> return 1;
> /* Otherwise falls through */
> default:
> @@ -3307,7 +3303,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> break;
> case MSR_IA32_BNDCFGS:
> if (!kvm_mpx_supported() ||
> - (!msr_info->host_initiated && !guest_cpuid_has_mpx(vcpu)))
> + (!msr_info->host_initiated &&
> + !guest_cpuid_has(vcpu, X86_FEATURE_MPX)))
> return 1;
> if (is_noncanonical_address(data & PAGE_MASK) ||
> (data & MSR_IA32_BNDCFGS_RSVD))
> @@ -3370,7 +3367,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> clear_atomic_switch_msr(vmx, MSR_IA32_XSS);
> break;
> case MSR_TSC_AUX:
> - if (!guest_cpuid_has_rdtscp(vcpu) && !msr_info->host_initiated)
> + if (!msr_info->host_initiated &&
> + !guest_cpuid_has(vcpu, X86_FEATURE_MPX))

dito

> return 1;
> /* Check reserved bit, higher 32 bits should be zero */
> if ((data >> 32) != 0)
> @@ -9383,7 +9381,7 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> u32 secondary_exec_ctl = vmx_secondary_exec_control(vmx);
>
> if (vmx_rdtscp_supported()) {
> - bool rdtscp_enabled = guest_cpuid_has_rdtscp(vcpu);
> + bool rdtscp_enabled = guest_cpuid_has(vcpu, X86_FEATURE_MPX);

dito

> if (!rdtscp_enabled)

--

Thanks,

David