[RFC,06/10] KVM: VMX: Added handle of SPP write protection fault.

Commit Message

Zhang, Yi Oct. 13, 2017, 11:14 p.m. UTC

From: Zhang Yi Z <[e-mail]>

A control bit in EPT leaf paging-structure entries is defined as
“Sub-Page Permission” (SPP bit). The bit position is 61

While hardware walking the SPP page table, If the sub-page
region write permission bit is set, the write is allowed,
else the write is disallowed and results in an EPT violation.

we need peek this case in EPT violation handler, and trigger
a user-space exit, return the write protected address(GPA)
to user(qemu).

Signed-off-by: Zhang Yi Z <[e-mail]>
Signed-off-by: He Chen <[e-mail]>
---
 arch/x86/kvm/mmu.c       | 19 +++++++++++++++++++
 arch/x86/kvm/mmu.h       |  1 +
 include/uapi/linux/kvm.h |  5 +++++
 3 files changed, 25 insertions(+)

Patch

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 32a374c..1fbe467 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3232,6 +3232,21 @@  static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 		if ((error_code & PFERR_WRITE_MASK) &&
 		    spte_can_locklessly_be_made_writable(spte))
 		{
+			/*
+			 * Record write protect fault caused by
+			 * Sub-page Protection
+			 */
+			if (spte & PT_SPP_MASK) {
+				fault_handled = true;
+
+				vcpu->run->exit_reason = KVM_EXIT_SPP;
+				vcpu->run->spp.addr = gva;
+				kvm_skip_emulated_instruction(vcpu);
+
+				/* Let QEMU decide how to handle this. */
+				break;
+			}
+
 			new_spte |= PT_WRITABLE_MASK;
 
 			/*
@@ -4966,6 +4981,10 @@  int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
 
 	r = vcpu->arch.mmu.page_fault(vcpu, cr2, lower_32_bits(error_code),
 				      false);
+
+	if (vcpu->run->exit_reason == KVM_EXIT_SPP)
+		return 0;
+
 	if (r < 0)
 		return r;
 	if (!r)
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 64a2dbd..c860efe 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -25,6 +25,7 @@ 
 #define PT_PAGE_SIZE_MASK (1ULL << PT_PAGE_SIZE_SHIFT)
 #define PT_PAT_MASK (1ULL << 7)
 #define PT_GLOBAL_MASK (1ULL << 8)
+#define PT_SPP_MASK (1ULL << 61)
 #define PT64_NX_SHIFT 63
 #define PT64_NX_MASK (1ULL << PT64_NX_SHIFT)
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 8388875..0cd821e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -234,6 +234,7 @@  struct kvm_hyperv_exit {
 #define KVM_EXIT_S390_STSI        25
 #define KVM_EXIT_IOAPIC_EOI       26
 #define KVM_EXIT_HYPERV           27
+#define KVM_EXIT_SPP              28
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
@@ -389,6 +390,10 @@  struct kvm_run {
 		struct {
 			__u8 vector;
 		} eoi;
+		/* KVM_EXIT_SPP */
+		struct {
+			__u64 addr;
+		} spp;
 		/* KVM_EXIT_HYPERV */
 		struct kvm_hyperv_exit hyperv;
 		/* Fix the size of the union. */