Re: [PATCH v2 1/3] KVM: x86: Add EMULTYPE_PF when emulation is triggered by a page fault
From: Xiaoyao Li
Date: Thu Feb 20 2020 - 21:59:29 EST
On 2/21/2020 4:11 AM, Sean Christopherson wrote:
On Wed, Feb 19, 2020 at 05:01:41PM +0800, Xiaoyao Li wrote:
On 2/19/2020 7:03 AM, Sean Christopherson wrote:
Add a new emulation type flag to explicitly mark emulation related to a
page fault. Move the propation of the GPA into the emulator from the
page fault handler into x86_emulate_instruction, using EMULTYPE_PF as an
indicator that cr2 is valid. Similarly, don't propagate cr2 into the
exception.address when it's *not* valid.
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 12 +++++++++---
arch/x86/kvm/mmu/mmu.c | 10 ++--------
arch/x86/kvm/x86.c | 25 +++++++++++++++++++------
3 files changed, 30 insertions(+), 17 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4dffbc10d3f8..10c1e8f472b6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1370,8 +1370,9 @@ extern u64 kvm_mce_cap_supported;
* decode the instruction length. For use *only* by
* kvm_x86_ops->skip_emulated_instruction() implementations.
*
- * EMULTYPE_ALLOW_RETRY - Set when the emulator should resume the guest to
- * retry native execution under certain conditions.
+ * EMULTYPE_ALLOW_RETRY_PF - Set when the emulator should resume the guest to
+ * retry native execution under certain conditions,
+ * Can only be set in conjunction with EMULTYPE_PF.
*
* EMULTYPE_TRAP_UD_FORCED - Set when emulating an intercepted #UD that was
* triggered by KVM's magic "force emulation" prefix,
@@ -1384,13 +1385,18 @@ extern u64 kvm_mce_cap_supported;
* backdoor emulation, which is opt in via module param.
* VMware backoor emulation handles select instructions
* and reinjects the #GP for all other cases.
+ *
+ * EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
+ * case the CR2/GPA value pass on the stack is valid.
*/
#define EMULTYPE_NO_DECODE (1 << 0)
#define EMULTYPE_TRAP_UD (1 << 1)
#define EMULTYPE_SKIP (1 << 2)
-#define EMULTYPE_ALLOW_RETRY (1 << 3)
+#define EMULTYPE_ALLOW_RETRY_PF (1 << 3)
How about naming it as EMULTYPE_PF_ALLOW_RETRY and exchanging the bit
position with EMULTYPE_PF ?
Hmm, EMULTYPE_PF_ALLOW_RETRY does sound better. I'm on the fence regarding
shuffling the bits. If I were to shuffle the bits, I'd do a more thorough
reorder so that the #UD and #PF types are consecutive, e.g.
#define EMULTYPE_NO_DECODE (1 << 0)
#define EMULTYPE_TRAP_UD (1 << 1)
#define EMULTYPE_TRAP_UD_FORCED (1 << 2)
#define EMULTYPE_SKIP (1 << 3)
#define EMULTYPE_VMWARE_GP (1 << 4)
#define EMULTYPE_PF (1 << 5)
#define EMULTYPE_PF_ALLOW_RETRY (1 << 6)
Part of me really wants to do that, the other part of me thinks it's
unnecessary thrash.
I'm fine with thorough reorder, it helps read the codes.
It's up to Paolo, anyway.
#define EMULTYPE_TRAP_UD_FORCED (1 << 4)
#define EMULTYPE_VMWARE_GP (1 << 5)
+#define EMULTYPE_PF (1 << 6)
+
int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
void *insn, int insn_len);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7011a4e54866..258624d46588 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5416,18 +5416,12 @@ EXPORT_SYMBOL_GPL(kvm_mmu_unprotect_page_virt);
int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
void *insn, int insn_len)
{
- int r, emulation_type = 0;
+ int r, emulation_type = EMULTYPE_PF;
bool direct = vcpu->arch.mmu->direct_map;
if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
return RET_PF_RETRY;
- /* With shadow page tables, fault_address contains a GVA or nGPA. */
- if (vcpu->arch.mmu->direct_map) {
- vcpu->arch.gpa_available = true;
- vcpu->arch.gpa_val = cr2_or_gpa;
- }
-
r = RET_PF_INVALID;
if (unlikely(error_code & PFERR_RSVD_MASK)) {
r = handle_mmio_page_fault(vcpu, cr2_or_gpa, direct);
@@ -5472,7 +5466,7 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
* for L1 isn't going to magically fix whatever issue cause L2 to fail.
*/
if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
- emulation_type = EMULTYPE_ALLOW_RETRY;
+ emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
emulate:
/*
* On AMD platforms, under certain conditions insn_len may be zero on #NPF.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fbabb2f06273..92af6c5a69e3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6483,10 +6483,11 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
gpa_t gpa = cr2_or_gpa;
kvm_pfn_t pfn;
- if (!(emulation_type & EMULTYPE_ALLOW_RETRY))
+ if (!(emulation_type & EMULTYPE_ALLOW_RETRY_PF))
return false;
- if (WARN_ON_ONCE(is_guest_mode(vcpu)))
+ if (WARN_ON_ONCE(is_guest_mode(vcpu)) ||
+ WARN_ON_ONCE(!(emulation_type & EMULTYPE_PF)))
return false;
if (!vcpu->arch.mmu->direct_map) {
@@ -6574,10 +6575,11 @@ static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
*/
vcpu->arch.last_retry_eip = vcpu->arch.last_retry_addr = 0;
- if (!(emulation_type & EMULTYPE_ALLOW_RETRY))
+ if (!(emulation_type & EMULTYPE_ALLOW_RETRY_PF))
return false;
- if (WARN_ON_ONCE(is_guest_mode(vcpu)))
+ if (WARN_ON_ONCE(is_guest_mode(vcpu)) ||
+ WARN_ON_ONCE(!(emulation_type & EMULTYPE_PF)))
return false;
if (x86_page_table_writing_insn(ctxt))
@@ -6830,8 +6832,19 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
}
restart:
- /* Save the faulting GPA (cr2) in the address field */
- ctxt->exception.address = cr2_or_gpa;
+ if (emulation_type & EMULTYPE_PF) {
+ /* Save the faulting GPA (cr2) in the address field */
+ ctxt->exception.address = cr2_or_gpa;
+
+ /* With shadow page tables, cr2 contains a GVA or nGPA. */
+ if (vcpu->arch.mmu->direct_map) {
+ vcpu->arch.gpa_available = true;
+ vcpu->arch.gpa_val = cr2_or_gpa;
+ }
+ } else {
+ /* Sanitize the address out of an abundance of paranoia. */
+ ctxt->exception.address = 0;
+ }
r = x86_emulate_insn(ctxt);