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Date: Mon, 18 Oct 2021 15:08:35 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/7] KVM: VMX: Only context switch some PT MSRs when
they exist
On 27/08/21 09:02, Xiaoyao Li wrote:
> The enumeration of Intel PT feature doesn't guarantee the existence of
> MSR_IA32_RTIT_OUTPUT_BASE, MSR_IA32_RTIT_OUTPUT_MASK and
> MSR_IA32_RTIT_CR3_MATCH. They need to be detected from CPUID 0x14 PT
> leaves.
>
> Detect the existence of them in hardware_setup() and only context switch
> them when they exist. Otherwise it will cause #GP when access them.
If intel_pt_validate_hw_cap is not fast enough, it should be optimized.
Something like this:
diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 7f406c14715f..9c7167dcb719 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -41,13 +41,15 @@ static struct pt_pmu pt_pmu;
* permitted values for certain bit fields).
*/
#define PT_CAP(_n, _l, _r, _m) \
- [PT_CAP_ ## _n] = { .name = __stringify(_n), .leaf = _l, \
- .reg = _r, .mask = _m }
+ [PT_CAP_ ## _n] = { .name = __stringify(_n), \
+ .index = _l * PT_CPUID_REGS_NUM + _r, \
+ .shift = __CONSTANT_FFS_32(_m), \
+ .mask = _m }
static struct pt_cap_desc {
const char *name;
- u32 leaf;
- u8 reg;
+ u16 index;
+ u8 shift;
u32 mask;
} pt_caps[] = {
PT_CAP(max_subleaf, 0, CPUID_EAX, 0xffffffff),
@@ -71,10 +73,8 @@ static struct pt_cap_desc {
u32 intel_pt_validate_cap(u32 *caps, enum pt_capabilities capability)
{
struct pt_cap_desc *cd = &pt_caps[capability];
- u32 c = caps[cd->leaf * PT_CPUID_REGS_NUM + cd->reg];
- unsigned int shift = __ffs(cd->mask);
- return (c & cd->mask) >> shift;
+ return (caps[cd->index] & cd->mask) >> cd->shift;
}
EXPORT_SYMBOL_GPL(intel_pt_validate_cap);
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 5e62e2383b7f..b4ee28d91b77 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -211,6 +211,17 @@ static inline int get_count_order_long(unsigned long l)
return (int)fls_long(--l);
}
+#define __CONSTANT_FFS_2(w) \
+ (((w) & 1) == 0)
+#define __CONSTANT_FFS_4(w) \
+ (((w) & 0x3) == 0 ? 2 + __CONSTANT_FFS_2((w) >> 2) : __CONSTANT_FFS_2((w)))
+#define __CONSTANT_FFS_8(w) \
+ (((w) & 0xf) == 0 ? 4 + __CONSTANT_FFS_4((w) >> 4) : __CONSTANT_FFS_4((w)))
+#define __CONSTANT_FFS_16(w) \
+ (((w) & 0xff) == 0 ? 8 + __CONSTANT_FFS_8((w) >> 8) : __CONSTANT_FFS_8((w)))
+#define __CONSTANT_FFS_32(w) \
+ (((w) & 0xffff) == 0 ? 16 + __CONSTANT_FFS_16((w) >> 16) : __CONSTANT_FFS_16((w)))
+
/**
* __ffs64 - find first set bit in a 64 bit word
* @word: The 64 bit word
Paolo
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
> arch/x86/kvm/vmx/vmx.c | 28 +++++++++++++++++++++-------
> 1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 394ef4732838..6819fc470072 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -204,6 +204,9 @@ module_param(ple_window_max, uint, 0444);
> int __read_mostly pt_mode = PT_MODE_SYSTEM;
> module_param(pt_mode, int, S_IRUGO);
>
> +static bool has_msr_rtit_cr3_match;
> +static bool has_msr_rtit_output_x;
> +
> static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
> static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
> static DEFINE_MUTEX(vmx_l1d_flush_mutex);
> @@ -1035,9 +1038,12 @@ static inline void pt_load_msr(struct pt_ctx *ctx, u32 addr_range)
> u32 i;
>
> wrmsrl(MSR_IA32_RTIT_STATUS, ctx->status);
> - wrmsrl(MSR_IA32_RTIT_OUTPUT_BASE, ctx->output_base);
> - wrmsrl(MSR_IA32_RTIT_OUTPUT_MASK, ctx->output_mask);
> - wrmsrl(MSR_IA32_RTIT_CR3_MATCH, ctx->cr3_match);
> + if (has_msr_rtit_output_x) {
> + wrmsrl(MSR_IA32_RTIT_OUTPUT_BASE, ctx->output_base);
> + wrmsrl(MSR_IA32_RTIT_OUTPUT_MASK, ctx->output_mask);
> + }
> + if (has_msr_rtit_cr3_match)
> + wrmsrl(MSR_IA32_RTIT_CR3_MATCH, ctx->cr3_match);
> for (i = 0; i < addr_range; i++) {
> wrmsrl(MSR_IA32_RTIT_ADDR0_A + i * 2, ctx->addr_a[i]);
> wrmsrl(MSR_IA32_RTIT_ADDR0_B + i * 2, ctx->addr_b[i]);
> @@ -1049,9 +1055,12 @@ static inline void pt_save_msr(struct pt_ctx *ctx, u32 addr_range)
> u32 i;
>
> rdmsrl(MSR_IA32_RTIT_STATUS, ctx->status);
> - rdmsrl(MSR_IA32_RTIT_OUTPUT_BASE, ctx->output_base);
> - rdmsrl(MSR_IA32_RTIT_OUTPUT_MASK, ctx->output_mask);
> - rdmsrl(MSR_IA32_RTIT_CR3_MATCH, ctx->cr3_match);
> + if (has_msr_rtit_output_x) {
> + rdmsrl(MSR_IA32_RTIT_OUTPUT_BASE, ctx->output_base);
> + rdmsrl(MSR_IA32_RTIT_OUTPUT_MASK, ctx->output_mask);
> + }
> + if (has_msr_rtit_cr3_match)
> + rdmsrl(MSR_IA32_RTIT_CR3_MATCH, ctx->cr3_match);
> for (i = 0; i < addr_range; i++) {
> rdmsrl(MSR_IA32_RTIT_ADDR0_A + i * 2, ctx->addr_a[i]);
> rdmsrl(MSR_IA32_RTIT_ADDR0_B + i * 2, ctx->addr_b[i]);
> @@ -7883,8 +7892,13 @@ static __init int hardware_setup(void)
>
> if (pt_mode != PT_MODE_SYSTEM && pt_mode != PT_MODE_HOST_GUEST)
> return -EINVAL;
> - if (!enable_ept || !cpu_has_vmx_intel_pt())
> + if (!enable_ept || !cpu_has_vmx_intel_pt()) {
> pt_mode = PT_MODE_SYSTEM;
> + } else if (boot_cpu_has(X86_FEATURE_INTEL_PT)) {
> + has_msr_rtit_cr3_match = intel_pt_validate_hw_cap(PT_CAP_cr3_filtering);
> + has_msr_rtit_output_x = intel_pt_validate_hw_cap(PT_CAP_topa_output) ||
> + intel_pt_validate_hw_cap(PT_CAP_single_range_output);
> + }
>
> setup_default_sgx_lepubkeyhash();
>
>
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