[Xen-devel] [PATCH v5 2/3] x86/mem_event: Deliver gla fault EPT violation information

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

On Intel EPT the exit qualification generated by a violation also includes a 
bit (EPT_GLA_FAULT) which describes the following information:
Set if the access causing the EPT violation is to a guest-physical address that 
is the translation of a linear address. Clear if the access causing the EPT 
violation is to a paging-structure entry as part of a page walk or the update 
of an accessed or dirty bit.

For more information see Table 27-7 in the Intel SDM.

This patch extends the mem_event system to deliver this extra information, 
which could be useful for determining the cause of a violation.

v5: Add missing bits to the SVM side, style fixes and switching to shared 
struct+enum in mm.h.
v4: Use new bitmaps to pass information.
v3: Style fixes.
v2: Split gla_fault into fault_in_gpt and fault_gla to be more compatible with 
the AMD implementation.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
---
 xen/arch/x86/hvm/svm/svm.c        |  7 ++++++-
 xen/arch/x86/hvm/vmx/vmx.c        |  4 ++++
 xen/arch/x86/mm/p2m.c             |  4 ++++
 xen/include/asm-x86/hvm/svm/svm.h |  6 ++++++
 xen/include/asm-x86/mm.h          | 11 +++++++++++
 xen/include/public/mem_event.h    |  4 +++-
 6 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index a7fac00..74fd386 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1394,7 +1394,7 @@ const struct hvm_function_table * __init start_svm(void)
 }
 
 static void svm_do_nested_pgfault(struct vcpu *v,
-    struct cpu_user_regs *regs, uint32_t pfec, paddr_t gpa)
+    struct cpu_user_regs *regs, uint64_t pfec, paddr_t gpa)
 {
     int ret;
     unsigned long gfn = gpa >> PAGE_SHIFT;
@@ -1409,6 +1409,11 @@ static void svm_do_nested_pgfault(struct vcpu *v,
         .insn_fetch = !!(pfec & PFEC_insn_fetch)
     };
 
+    if ( pfec & NPT_FAULT_WITH_GLA )
+        npfec.extra_fault_info |= extra_fault_info_with_gla;
+    if ( pfec & NPT_FAULT_IN_GPT )
+        npfec.extra_fault_info |= extra_fault_info_in_gpt;
+
     ret = hvm_hap_nested_page_fault(gpa, ~0ul, npfec);
 
     if ( tb_init_done )
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 1b328dd..056db8d 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2379,6 +2379,10 @@ static void ept_handle_violation(unsigned long 
qualification, paddr_t gpa)
     {
         __vmread(GUEST_LINEAR_ADDRESS, &gla);
         npfec.gla_valid = 1;
+        if( qualification & EPT_GLA_FAULT )
+            npfec.extra_fault_info |= extra_fault_info_with_gla;
+        else
+            npfec.extra_fault_info |= extra_fault_info_in_gpt;
     }
     else
         gla = ~0ull;
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 34c792c..f99c691 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1405,6 +1405,10 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned long 
gla,
         req->offset = gpa & ((1 << PAGE_SHIFT) - 1);
         req->gla_valid = check.gla_valid;
         req->gla = gla;
+        if ( check.extra_fault_info & extra_fault_info_with_gla )
+            req->fault_with_gla = 1;
+        if ( check.extra_fault_info & extra_fault_info_in_gpt )
+            req->fault_in_gpt = 1;
         req->access_r = check.read_access;
         req->access_w = check.write_access;
         req->access_x = check.insn_fetch;
diff --git a/xen/include/asm-x86/hvm/svm/svm.h 
b/xen/include/asm-x86/hvm/svm/svm.h
index 1ffe6d6..1a286ba 100644
--- a/xen/include/asm-x86/hvm/svm/svm.h
+++ b/xen/include/asm-x86/hvm/svm/svm.h
@@ -105,4 +105,10 @@ extern u32 svm_feature_flags;
 extern void svm_host_osvw_reset(void);
 extern void svm_host_osvw_init(void);
 
+/* EXITINFO1 fields on NPT faults */
+#define _NPT_FAULT_WITH_GLA     32
+#define NPT_FAULT_WITH_GLA      (1UL<<_NPT_FAULT_WITH_GLA)
+#define _NPT_FAULT_IN_GPT       33
+#define NPT_FAULT_IN_GPT        (1UL<<_NPT_FAULT_IN_GPT)
+
 #endif /* __ASM_X86_HVM_SVM_H__ */
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index 9327f99..1a9512a 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -552,6 +552,16 @@ void audit_domains(void);
 #endif
 
 /*
+ * Extra fault info types which are used to further describe
+ * the source of a mem access violation.
+ */
+typedef enum {
+    extra_fault_info_unavailable    = 0u,
+    extra_fault_info_in_gpt         = ( 1u << 0 ),
+    extra_fault_info_with_gla       = ( 1u << 1 ),
+} extra_fault_info_t;
+
+/*
  * Information used to perform mem access checks.
  */
 struct mem_access_check {
@@ -559,6 +569,7 @@ struct mem_access_check {
     unsigned int write_access:1;
     unsigned int insn_fetch:1;
     unsigned int gla_valid:1;
+    unsigned int extra_fault_info:2; /* extra_fault_info_t */
 };
 
 int new_guest_cr3(unsigned long pfn);
diff --git a/xen/include/public/mem_event.h b/xen/include/public/mem_event.h
index 3831b41..fc12697 100644
--- a/xen/include/public/mem_event.h
+++ b/xen/include/public/mem_event.h
@@ -62,7 +62,9 @@ typedef struct mem_event_st {
     uint16_t access_w:1;
     uint16_t access_x:1;
     uint16_t gla_valid:1;
-    uint16_t available:12;
+    uint16_t fault_with_gla:1;
+    uint16_t fault_in_gpt:1;
+    uint16_t available:10;
 
     uint16_t reason;
 } mem_event_request_t, mem_event_response_t;
-- 
2.0.1


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