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KVM: x86: Add support for reverse CPUID lookup of scattered features

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Introduce a scheme that allows KVM's CPUID magic to support features
that are scattered in the kernel's feature words.  To advertise and/or
query guest support for CPUID-based features, KVM requires the bit
number of an X86_FEATURE_* to match the bit number in its associated
CPUID entry.  For scattered features, this does not hold true.

Add a framework to allow defining KVM-only words, stored in
kvm_cpu_caps after the shared kernel caps, that can be used to gather
the scattered feature bits by translating X86_FEATURE_* flags into their
KVM-defined feature.

Note, because reverse_cpuid_check() effectively forces kvm_cpu_caps
lookups to be resolved at compile time, there is no runtime cost for
translating from kernel-defined to kvm-defined features.

More details here:  https://lkml.kernel.org/r/X/jxCOLG+HUO4QlZ@google.com

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Message-Id: <16cad8d00475f67867fb36701fc7fb7c1ec86ce1.1618196135.git.kai.huang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-04-12 16:21:35 +12:00 committed by Paolo Bonzini
parent 00e7646c35
commit 4e66c0cb79
2 changed files with 61 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

32
arch/x86/kvm/cpuid.c
View file

@ -28,7 +28,7 @@
* Unlike "struct cpuinfo_x86.x86_capability", kvm_cpu_caps doesn't need to be
* aligned to sizeof(unsigned long) because it's not accessed via bitops.
*/
u32 kvm_cpu_caps[NCAPINTS] __read_mostly;
u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly;
EXPORT_SYMBOL_GPL(kvm_cpu_caps);
static u32 xstate_required_size(u64 xstate_bv, bool compacted)
@ -53,6 +53,7 @@ static u32 xstate_required_size(u64 xstate_bv, bool compacted)
}
#define F feature_bit
#define SF(name) (boot_cpu_has(X86_FEATURE_##name) ? F(name) : 0)
static inline struct kvm_cpuid_entry2 *cpuid_entry2_find(
struct kvm_cpuid_entry2 *entries, int nent, u32 function, u32 index)
@ -347,13 +348,13 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
return r;
}
static __always_inline void kvm_cpu_cap_mask(enum cpuid_leafs leaf, u32 mask)
/* Mask kvm_cpu_caps for @leaf with the raw CPUID capabilities of this CPU. */
static __always_inline void __kvm_cpu_cap_mask(enum cpuid_leafs leaf)
{
const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32);
struct kvm_cpuid_entry2 entry;
reverse_cpuid_check(leaf);
kvm_cpu_caps[leaf] &= mask;
cpuid_count(cpuid.function, cpuid.index,
&entry.eax, &entry.ebx, &entry.ecx, &entry.edx);
@ -361,6 +362,26 @@ static __always_inline void kvm_cpu_cap_mask(enum cpuid_leafs leaf, u32 mask)
kvm_cpu_caps[leaf] &= *__cpuid_entry_get_reg(&entry, cpuid.reg);
}
static __always_inline void kvm_cpu_cap_init_scattered(enum cpuid_leafs leaf, u32 mask)
{
/* Use kvm_cpu_cap_mask for non-scattered leafs. */
BUILD_BUG_ON(leaf < NCAPINTS);
kvm_cpu_caps[leaf] = mask;
__kvm_cpu_cap_mask(leaf);
}
static __always_inline void kvm_cpu_cap_mask(enum cpuid_leafs leaf, u32 mask)
{
/* Use kvm_cpu_cap_init_scattered for scattered leafs. */
BUILD_BUG_ON(leaf >= NCAPINTS);
kvm_cpu_caps[leaf] &= mask;
__kvm_cpu_cap_mask(leaf);
}
void kvm_set_cpu_caps(void)
{
unsigned int f_nx = is_efer_nx() ? F(NX) : 0;
@ -371,12 +392,13 @@ void kvm_set_cpu_caps(void)
unsigned int f_gbpages = 0;
unsigned int f_lm = 0;
#endif
memset(kvm_cpu_caps, 0, sizeof(kvm_cpu_caps));
BUILD_BUG_ON(sizeof(kvm_cpu_caps) >
BUILD_BUG_ON(sizeof(kvm_cpu_caps) - (NKVMCAPINTS * sizeof(*kvm_cpu_caps)) >
sizeof(boot_cpu_data.x86_capability));
memcpy(&kvm_cpu_caps, &boot_cpu_data.x86_capability,
sizeof(kvm_cpu_caps));
sizeof(kvm_cpu_caps) - (NKVMCAPINTS * sizeof(*kvm_cpu_caps)));
kvm_cpu_cap_mask(CPUID_1_ECX,
/*

39
arch/x86/kvm/cpuid.h
View file

@ -7,7 +7,20 @@
#include <asm/processor.h>
#include <uapi/asm/kvm_para.h>
extern u32 kvm_cpu_caps[NCAPINTS] __read_mostly;
/*
* Hardware-defined CPUID leafs that are scattered in the kernel, but need to
* be directly used by KVM. Note, these word values conflict with the kernel's
* "bug" caps, but KVM doesn't use those.
*/
enum kvm_only_cpuid_leafs {
NR_KVM_CPU_CAPS = NCAPINTS,
NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,
};
#define X86_KVM_FEATURE(w, f) ((w)*32 + (f))
extern u32 kvm_cpu_caps[NR_KVM_CPU_CAPS] __read_mostly;
void kvm_set_cpu_caps(void);
void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu);
@ -100,6 +113,20 @@ static __always_inline void reverse_cpuid_check(unsigned int x86_leaf)
BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
}
/*
* Translate feature bits that are scattered in the kernel's cpufeatures word
* into KVM feature words that align with hardware's definitions.
*/
static __always_inline u32 __feature_translate(int x86_feature)
{
return x86_feature;
}
static __always_inline u32 __feature_leaf(int x86_feature)
{
return __feature_translate(x86_feature) / 32;
}
/*
* Retrieve the bit mask from an X86_FEATURE_* definition. Features contain
* the hardware defined bit number (stored in bits 4:0) and a software defined
@ -108,6 +135,8 @@ static __always_inline void reverse_cpuid_check(unsigned int x86_leaf)
*/
static __always_inline u32 __feature_bit(int x86_feature)
{
x86_feature = __feature_translate(x86_feature);
reverse_cpuid_check(x86_feature / 32);
return 1 << (x86_feature & 31);
}
@ -116,7 +145,7 @@ static __always_inline u32 __feature_bit(int x86_feature)
static __always_inline struct cpuid_reg x86_feature_cpuid(unsigned int x86_feature)
{
unsigned int x86_leaf = x86_feature / 32;
unsigned int x86_leaf = __feature_leaf(x86_feature);
reverse_cpuid_check(x86_leaf);
return reverse_cpuid[x86_leaf];
@ -316,7 +345,7 @@ static inline bool cpuid_fault_enabled(struct kvm_vcpu *vcpu)
static __always_inline void kvm_cpu_cap_clear(unsigned int x86_feature)
{
unsigned int x86_leaf = x86_feature / 32;
unsigned int x86_leaf = __feature_leaf(x86_feature);
reverse_cpuid_check(x86_leaf);
kvm_cpu_caps[x86_leaf] &= ~__feature_bit(x86_feature);
@ -324,7 +353,7 @@ static __always_inline void kvm_cpu_cap_clear(unsigned int x86_feature)
static __always_inline void kvm_cpu_cap_set(unsigned int x86_feature)
{
unsigned int x86_leaf = x86_feature / 32;
unsigned int x86_leaf = __feature_leaf(x86_feature);
reverse_cpuid_check(x86_leaf);
kvm_cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
@ -332,7 +361,7 @@ static __always_inline void kvm_cpu_cap_set(unsigned int x86_feature)
static __always_inline u32 kvm_cpu_cap_get(unsigned int x86_feature)
{
unsigned int x86_leaf = x86_feature / 32;
unsigned int x86_leaf = __feature_leaf(x86_feature);
reverse_cpuid_check(x86_leaf);
return kvm_cpu_caps[x86_leaf] & __feature_bit(x86_feature);