[Xen-devel] [PATCH v3] SVM: Add union intstat_t for offset 68h in vmcb struct

[Pu Wen <puwen@xxxxxxxx>]

According to chapter "Appendix B Layout of VMCB" in the new version
(v3.32) AMD64 APM[1], bit 1 of the VMCB offset 68h is defined as
GUEST_INTERRUPT_MASK.

In current xen codes, it use whole u64 interrupt_shadow to setup
interrupt shadow, which will misuse other bit in VMCB offset 68h
as part of interrupt_shadow, causing svm_get_interrupt_shadow() to
mistake the guest having interrupts enabled as being in an interrupt
shadow.  This has been observed to cause SeaBIOS to hang on boot.

Add union intstat_t for VMCB offset 68h and fix codes to only use
bit 0 as intr_shadow according to the new APM description.

Reference:
[1] https://www.amd.com/system/files/TechDocs/24593.pdf

Signed-off-by: Pu Wen <puwen@xxxxxxxx>
---
v2->v3:
  - Use bool for bit[0:1] and drop the resvd field.
  - Add description about breaking guest.

v1->v2:
  - Copy the whole int_stat in nsvm_vmcb_prepare4vmrun() and
    nsvm_vmcb_prepare4vmexit().
  - Dump all 64 bits of int_stat in svm_vmcb_dump().

 xen/arch/x86/hvm/svm/nestedsvm.c   |  8 ++++----
 xen/arch/x86/hvm/svm/svm.c         |  8 ++++----
 xen/arch/x86/hvm/svm/svmdebug.c    |  4 ++--
 xen/include/asm-x86/hvm/svm/vmcb.h | 10 +++++++++-
 4 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/nestedsvm.c b/xen/arch/x86/hvm/svm/nestedsvm.c
index 3bd2a119d3..bbd06e342e 100644
--- a/xen/arch/x86/hvm/svm/nestedsvm.c
+++ b/xen/arch/x86/hvm/svm/nestedsvm.c
@@ -507,8 +507,8 @@ static int nsvm_vmcb_prepare4vmrun(struct vcpu *v, struct 
cpu_user_regs *regs)
         n2vmcb->_vintr.fields.intr_masking = 1;
     }
 
-    /* Shadow Mode */
-    n2vmcb->interrupt_shadow = ns_vmcb->interrupt_shadow;
+    /* Interrupt state */
+    n2vmcb->int_stat = ns_vmcb->int_stat;
 
     /* Exit codes */
     n2vmcb->exitcode = ns_vmcb->exitcode;
@@ -1057,8 +1057,8 @@ nsvm_vmcb_prepare4vmexit(struct vcpu *v, struct 
cpu_user_regs *regs)
     if (!(svm->ns_hostflags.fields.vintrmask))
         ns_vmcb->_vintr.fields.intr_masking = 0;
 
-    /* Shadow mode */
-    ns_vmcb->interrupt_shadow = n2vmcb->interrupt_shadow;
+    /* Interrupt state */
+    ns_vmcb->int_stat = n2vmcb->int_stat;
 
     /* Exit codes */
     ns_vmcb->exitcode = n2vmcb->exitcode;
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 32d8d847f2..888f504a94 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -116,7 +116,7 @@ void __update_guest_eip(struct cpu_user_regs *regs, 
unsigned int inst_len)
     regs->rip += inst_len;
     regs->eflags &= ~X86_EFLAGS_RF;
 
-    curr->arch.hvm.svm.vmcb->interrupt_shadow = 0;
+    curr->arch.hvm.svm.vmcb->int_stat.intr_shadow = 0;
 
     if ( regs->eflags & X86_EFLAGS_TF )
         hvm_inject_hw_exception(TRAP_debug, X86_EVENT_NO_EC);
@@ -432,7 +432,7 @@ static unsigned int svm_get_interrupt_shadow(struct vcpu *v)
     struct vmcb_struct *vmcb = v->arch.hvm.svm.vmcb;
     unsigned int intr_shadow = 0;
 
-    if ( vmcb->interrupt_shadow )
+    if ( vmcb->int_stat.intr_shadow )
         intr_shadow |= HVM_INTR_SHADOW_MOV_SS | HVM_INTR_SHADOW_STI;
 
     if ( vmcb_get_general1_intercepts(vmcb) & GENERAL1_INTERCEPT_IRET )
@@ -446,7 +446,7 @@ static void svm_set_interrupt_shadow(struct vcpu *v, 
unsigned int intr_shadow)
     struct vmcb_struct *vmcb = v->arch.hvm.svm.vmcb;
     u32 general1_intercepts = vmcb_get_general1_intercepts(vmcb);
 
-    vmcb->interrupt_shadow =
+    vmcb->int_stat.intr_shadow =
         !!(intr_shadow & (HVM_INTR_SHADOW_MOV_SS|HVM_INTR_SHADOW_STI));
 
     general1_intercepts &= ~GENERAL1_INTERCEPT_IRET;
@@ -2945,7 +2945,7 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
          * retired.
          */
         general1_intercepts &= ~GENERAL1_INTERCEPT_IRET;
-        vmcb->interrupt_shadow = 1;
+        vmcb->int_stat.intr_shadow = 1;
 
         vmcb_set_general1_intercepts(vmcb, general1_intercepts);
         break;
diff --git a/xen/arch/x86/hvm/svm/svmdebug.c b/xen/arch/x86/hvm/svm/svmdebug.c
index 366a003f21..5aa9d410ba 100644
--- a/xen/arch/x86/hvm/svm/svmdebug.c
+++ b/xen/arch/x86/hvm/svm/svmdebug.c
@@ -51,9 +51,9 @@ void svm_vmcb_dump(const char *from, const struct vmcb_struct 
*vmcb)
     printk("iopm_base_pa = %#"PRIx64" msrpm_base_pa = %#"PRIx64" tsc_offset = 
%#"PRIx64"\n",
            vmcb_get_iopm_base_pa(vmcb), vmcb_get_msrpm_base_pa(vmcb),
            vmcb_get_tsc_offset(vmcb));
-    printk("tlb_control = %#x vintr = %#"PRIx64" interrupt_shadow = 
%#"PRIx64"\n",
+    printk("tlb_control = %#x vintr = %#"PRIx64" int_stat = %#"PRIx64"\n",
            vmcb->tlb_control, vmcb_get_vintr(vmcb).bytes,
-           vmcb->interrupt_shadow);
+           vmcb->int_stat.raw);
     printk("event_inj %016"PRIx64", valid? %d, ec? %d, type %u, vector %#x\n",
            vmcb->event_inj.raw, vmcb->event_inj.v,
            vmcb->event_inj.ev, vmcb->event_inj.type,
diff --git a/xen/include/asm-x86/hvm/svm/vmcb.h 
b/xen/include/asm-x86/hvm/svm/vmcb.h
index b9e389d481..58eafe3b23 100644
--- a/xen/include/asm-x86/hvm/svm/vmcb.h
+++ b/xen/include/asm-x86/hvm/svm/vmcb.h
@@ -316,6 +316,14 @@ typedef union
     uint64_t raw;
 } intinfo_t;
 
+typedef union {
+    struct {
+        bool intr_shadow:    1;
+        bool guest_intr_mask:1;
+    };
+    uint64_t raw;
+} intstat_t;
+
 typedef union
 {
     u64 bytes;
@@ -414,7 +422,7 @@ struct vmcb_struct {
     u8  tlb_control;            /* offset 0x5C */
     u8  res07[3];
     vintr_t _vintr;             /* offset 0x60 - cleanbit 3 */
-    u64 interrupt_shadow;       /* offset 0x68 */
+    intstat_t int_stat;         /* offset 0x68 */
     u64 exitcode;               /* offset 0x70 */
     union {
         struct {
-- 
2.23.0