[Xen-devel] [PATCH RFC 04/14] xen: vmx: Introduce SPP-Induced vm exit and it's handle.

[Zhang Yi <yi.z.zhang@xxxxxxxxxxxxxxx>]

From: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>

Accesses using guest-physical addresses may cause SPP-induced VM exits
due to an SPPT misconfiguration or an
SPPT miss. The basic VM exit reason code reported for SPP-induced VM
exits is 66.

An SPPT misconfiguration VM exit occurs when, in the course of
translating a guest-physical address, the logical processor encounters
a leaf EPT paging-structure entry mapping a 4KB page for which the
sub-page write permission control bit is set and during the SPPT lookup
an SPPT paging-structure entry contains an unsupported value.

An SPPT miss VM exit occurs when, in the course of translation a
guest-physical address, the logical processor encounters a leaf
EPT paging-structure entry for which the sub-page write permission
control bit is set and during the SPPT lookup there is no SPPT
misconfiguration but any level of SPPT paging-structure entries
are not-present.

Also Introduced the new exit qualification for SPPT-induced vmexits.

| Bit   | Contents                                                          |
| :---- | :---------------------------------------------------------------- |
| 10:0  | Reserved (0).                                                     |
| 11    | SPPT VM exit type. Set for SPPT Miss, cleared for SPPT Misconfig. |
| 12    | NMI unblocking due to IRET                                        |
| 63:13 | Reserved (0)                                                      |

Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c        | 31 +++++++++++++++++++++++++++++++
 xen/include/asm-x86/hvm/vmx/vmx.h | 11 +++++++++++
 2 files changed, 42 insertions(+)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 69ce3aa..04ae0d6 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -3521,6 +3521,28 @@ static int vmx_handle_apic_write(void)
     return vlapic_apicv_write(current, exit_qualification & 0xfff);
 }
 
+static int vmx_handle_spp(spp_qual_t q, paddr_t gpa)
+{
+    if ( q.sppt_miss_type )
+    {
+        /*
+         * SPPT Miss :
+         * Subpage Protection Table not present
+         */
+        printk("SPP miss occured at gpa:%lx\n", gpa);
+
+        return true;
+    }
+
+    /*
+     * SPPT Misconfig
+     * This is probably possible that your sppt table
+     * set as a incorrect format
+     */
+    WARN_ON(1);
+    return false;
+}
+
 void vmx_vmexit_handler(struct cpu_user_regs *regs)
 {
     unsigned long exit_qualification, exit_reason, idtv_info, intr_info = 0;
@@ -4124,6 +4146,15 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
     case EXIT_REASON_ACCESS_LDTR_OR_TR:
         vmx_handle_descriptor_access(exit_reason);
         break;
+    case EXIT_REASON_SPP:
+    {
+        paddr_t gpa;
+
+        __vmread(GUEST_PHYSICAL_ADDRESS, &gpa);
+        __vmread(EXIT_QUALIFICATION, &exit_qualification);
+        vmx_handle_spp(exit_qualification, gpa);
+        break;
+    }
 
     case EXIT_REASON_VMX_PREEMPTION_TIMER_EXPIRED:
     case EXIT_REASON_INVPCID:
diff --git a/xen/include/asm-x86/hvm/vmx/vmx.h 
b/xen/include/asm-x86/hvm/vmx/vmx.h
index 4889a64..35aada6 100644
--- a/xen/include/asm-x86/hvm/vmx/vmx.h
+++ b/xen/include/asm-x86/hvm/vmx/vmx.h
@@ -213,6 +213,7 @@ static inline void pi_clear_sn(struct pi_desc *pi_desc)
 #define EXIT_REASON_PML_FULL            62
 #define EXIT_REASON_XSAVES              63
 #define EXIT_REASON_XRSTORS             64
+#define EXIT_REASON_SPP                 66
 
 /*
  * Interruption-information format
@@ -616,6 +617,16 @@ typedef union ept_qual {
     };
 } __transparent__ ept_qual_t;
 
+/* SPP induced vmexit qualifications definitions */
+typedef union spp_qual {
+    unsigned long raw;
+    struct {
+        unsigned long reserved   :11;
+        bool sppt_miss_type      :1;
+        unsigned long reserved2  :52;
+    };
+} __transparent__ spp_qual_t;
+
 #define EPT_L4_PAGETABLE_SHIFT      39
 #define EPT_PAGETABLE_ENTRIES       512
 
-- 
2.7.4


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