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x86/speculation: Use ARCH_CAPABILITIES to skip L1D flush on vmentry

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Bit 3 of ARCH_CAPABILITIES tells a hypervisor that L1D flush on vmentry is
not needed.  Add a new value to enum vmx_l1d_flush_state, which is used
either if there is no L1TF bug at all, or if bit 3 is set in ARCH_CAPABILITIES.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Paolo Bonzini 2018-08-05 16:07:46 +02:00 committed by Thomas Gleixner
parent ea156d192f
commit 8e0b2b9166
4 changed files with 13 additions and 0 deletions
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1
arch/x86/include/asm/msr-index.h
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@ -70,6 +70,7 @@
#define MSR_IA32_ARCH_CAPABILITIES 0x0000010a
#define ARCH_CAP_RDCL_NO (1 << 0) /* Not susceptible to Meltdown */
#define ARCH_CAP_IBRS_ALL (1 << 1) /* Enhanced IBRS support */
#define ARCH_CAP_SKIP_VMENTRY_L1DFLUSH (1 << 3) /* Skip L1D flush on vmentry */
#define ARCH_CAP_SSB_NO (1 << 4) /*
* Not susceptible to Speculative Store Bypass
* attack, so no Speculative Store Bypass

1
arch/x86/include/asm/vmx.h
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@ -582,6 +582,7 @@ enum vmx_l1d_flush_state {
VMENTER_L1D_FLUSH_COND,
VMENTER_L1D_FLUSH_ALWAYS,
VMENTER_L1D_FLUSH_EPT_DISABLED,
VMENTER_L1D_FLUSH_NOT_REQUIRED,
};
extern enum vmx_l1d_flush_state l1tf_vmx_mitigation;

1
arch/x86/kernel/cpu/bugs.c
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@ -755,6 +755,7 @@ static const char *l1tf_vmx_states[] = {
[VMENTER_L1D_FLUSH_COND] = "conditional cache flushes",
[VMENTER_L1D_FLUSH_ALWAYS] = "cache flushes",
[VMENTER_L1D_FLUSH_EPT_DISABLED] = "EPT disabled",
[VMENTER_L1D_FLUSH_NOT_REQUIRED] = "flush not necessary"
};
static ssize_t l1tf_show_state(char *buf)

10
arch/x86/kvm/vmx.c
View File

@ -218,6 +218,16 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
return 0;
}
if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES)) {
u64 msr;
rdmsrl(MSR_IA32_ARCH_CAPABILITIES, msr);
if (msr & ARCH_CAP_SKIP_VMENTRY_L1DFLUSH) {
l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
return 0;
}
}
/* If set to auto use the default l1tf mitigation method */
if (l1tf == VMENTER_L1D_FLUSH_AUTO) {
switch (l1tf_mitigation) {