[PATCH v3 6/8] kvm: x86: mmu: Do not use bit 63 for tracking special SPTEs

[Junaid Shahid <junaids@google.com>]

MMIO SPTEs currently set both bits 62 and 63 to distinguish them as special
PTEs. However, bit 63 is used as the SVE bit in Intel EPT PTEs. The SVE bit
is ignored for misconfigured PTEs but not necessarily for not-Present PTEs.
Since MMIO SPTEs use an EPT misconfiguration, so using bit 63 for them is
acceptable. However, the upcoming fast access tracking feature adds another
type of special tracking PTE, which uses not-Present PTEs and hence should
not set bit 63.

In order to use common bits to distinguish both type of special PTEs, we
now use only bit 62 as the special bit.

Signed-off-by: Junaid Shahid <junaids@google.com>
---
 arch/x86/include/asm/kvm_host.h | 7 +++++++
 arch/x86/include/asm/vmx.h      | 9 +++++++--
 arch/x86/kvm/vmx.c              | 6 +++---
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 77cb3f9..5a10eb7 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -208,6 +208,13 @@ enum {
 				 PFERR_WRITE_MASK |		\
 				 PFERR_PRESENT_MASK)
 
+/*
+ * The mask used to denote special SPTEs, which can be either MMIO SPTEs or
+ * Access Tracking SPTEs. We use bit 62 instead of bit 63 to avoid conflicting
+ * with the SVE bit in EPT PTEs.
+ */
+#define SPTE_SPECIAL_MASK (1ULL << 62)
+
 /* apic attention bits */
 #define KVM_APIC_CHECK_VAPIC	0
 /*
diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 659e402..45ee6d9 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -436,8 +436,13 @@ enum vmcs_field {
 #define VMX_EPT_WRITABLE_MASK			0x2ull
 #define VMX_EPT_EXECUTABLE_MASK			0x4ull
 #define VMX_EPT_IPAT_BIT    			(1ull << 6)
-#define VMX_EPT_ACCESS_BIT				(1ull << 8)
-#define VMX_EPT_DIRTY_BIT				(1ull << 9)
+#define VMX_EPT_ACCESS_BIT			(1ull << 8)
+#define VMX_EPT_DIRTY_BIT			(1ull << 9)
+
+/* The mask to use to trigger an EPT Misconfiguration in order to track MMIO */
+#define VMX_EPT_MISCONFIG_WX_VALUE           (VMX_EPT_WRITABLE_MASK |       \
+                                              VMX_EPT_EXECUTABLE_MASK)
+
 
 #define VMX_EPT_IDENTITY_PAGETABLE_ADDR		0xfffbc000ul
 
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index eb6b589..6a01e755 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4959,10 +4959,10 @@ static void ept_set_mmio_spte_mask(void)
 	/*
 	 * EPT Misconfigurations can be generated if the value of bits 2:0
 	 * of an EPT paging-structure entry is 110b (write/execute).
-	 * Also, magic bits (0x3ull << 62) is set to quickly identify mmio
-	 * spte.
+	 * Also, special bit (62) is set to quickly identify mmio spte.
 	 */
-	kvm_mmu_set_mmio_spte_mask((0x3ull << 62) | 0x6ull);
+	kvm_mmu_set_mmio_spte_mask(SPTE_SPECIAL_MASK |
+				   VMX_EPT_MISCONFIG_WX_VALUE);
 }
 
 #define VMX_XSS_EXIT_BITMAP 0
-- 
2.8.0.rc3.226.g39d4020