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

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>

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 0e75170..4731f0c 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -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

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 91241cc..95f9107 100644 (file)
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -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;

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b0886bd..86f4549 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -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)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8384f7c..29d6eab 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -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) {