From: Paolo Bonzini <pbonzini@redhat.com>
Date: Sun, 5 Aug 2018 16:07:46 +0200
Subject: x86/speculation: Use ARCH_CAPABILITIES to skip L1D flush on vmentry
Git-commit: 8e0b2b916662e09dd4d09e5271cdf214c6b80e62
Patch-mainline: v4.19-rc1
References: bsc#1106369

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>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/include/asm/msr-index.h |  1 +
 arch/x86/include/asm/vmx.h       |  1 +
 arch/x86/kernel/cpu/bugs.c       |  1 +
 arch/x86/kvm/vmx.c               | 10 ++++++++++
 4 files changed, 13 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 0e7517089b80..4731f0cf97c5 100644
--- 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 91241ccd4cfa..95f9107449bf 100644
--- 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 b0886bd24164..86f4549b7c9f 100644
--- 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 8384f7cb30d8..29d6eab6920e 100644
--- 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) {