[PATCH] x86/hvm: Include interruptibility state in hvm_hw_cpu

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

During VM fork resetting a failed vmentry has been observed when the reset
is performed immediately after a STI instruction executed. This is due to
the guest interruptibility state in the VMCS being modified by STI but the
subsequent reset removes the IF bit from FLAGS, causing the failed vmentry.

Include the interruptibility state information in the public hvm_hw_cpu struct
so that the CPU can be safely saved/restored.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c                 |  9 +++++----
 xen/arch/x86/hvm/vmx/vmx.c             |  4 ++++
 xen/arch/x86/include/asm/hvm/hvm.h     | 26 ++++++++++++++++++++++++++
 xen/include/public/arch-x86/hvm/save.h |  3 ++-
 4 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 709a4191ef..b239c72215 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -897,6 +897,8 @@ static int cf_check hvm_save_cpu_ctxt(struct vcpu *v, 
hvm_domain_context_t *h)
         ctxt.flags = XEN_X86_FPU_INITIALISED;
     }
 
+    ctxt.interruptibility_info = hvm_get_interrupt_shadow(v);
+
     return hvm_save_entry(CPU, v->vcpu_id, h, &ctxt);
 }
 
@@ -990,9 +992,6 @@ static int cf_check hvm_load_cpu_ctxt(struct domain *d, 
hvm_domain_context_t *h)
     if ( hvm_load_entry_zeroextend(CPU, h, &ctxt) != 0 )
         return -EINVAL;
 
-    if ( ctxt.pad0 != 0 )
-        return -EINVAL;
-
     /* Sanity check some control registers. */
     if ( (ctxt.cr0 & HVM_CR0_GUEST_RESERVED_BITS) ||
          !(ctxt.cr0 & X86_CR0_ET) ||
@@ -1155,6 +1154,8 @@ static int cf_check hvm_load_cpu_ctxt(struct domain *d, 
hvm_domain_context_t *h)
     v->arch.dr6   = ctxt.dr6;
     v->arch.dr7   = ctxt.dr7;
 
+    hvm_set_interrupt_shadow(v, ctxt.interruptibility_info);
+
     hvmemul_cancel(v);
 
     /* Auxiliary processors should be woken immediately. */
@@ -3888,7 +3889,7 @@ enum hvm_intblk hvm_interrupt_blocked(struct vcpu *v, 
struct hvm_intack intack)
          !(guest_cpu_user_regs()->eflags & X86_EFLAGS_IF) )
         return hvm_intblk_rflags_ie;
 
-    intr_shadow = alternative_call(hvm_funcs.get_interrupt_shadow, v);
+    intr_shadow = hvm_get_interrupt_shadow(v);
 
     if ( intr_shadow & (HVM_INTR_SHADOW_STI|HVM_INTR_SHADOW_MOV_SS) )
         return hvm_intblk_shadow;
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index c075370f64..e13817431a 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1323,7 +1323,9 @@ static unsigned int cf_check 
vmx_get_interrupt_shadow(struct vcpu *v)
 {
     unsigned long intr_shadow;
 
+    vmx_vmcs_enter(v);
     __vmread(GUEST_INTERRUPTIBILITY_INFO, &intr_shadow);
+    vmx_vmcs_exit(v);
 
     return intr_shadow;
 }
@@ -1331,7 +1333,9 @@ static unsigned int cf_check 
vmx_get_interrupt_shadow(struct vcpu *v)
 static void cf_check vmx_set_interrupt_shadow(
     struct vcpu *v, unsigned int intr_shadow)
 {
+    vmx_vmcs_enter(v);
     __vmwrite(GUEST_INTERRUPTIBILITY_INFO, intr_shadow);
+    vmx_vmcs_exit(v);
 }
 
 static void vmx_load_pdptrs(struct vcpu *v)
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h 
b/xen/arch/x86/include/asm/hvm/hvm.h
index 5b7ec0cf69..2fb7865a05 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -720,6 +720,22 @@ static inline int hvm_vmtrace_reset(struct vcpu *v)
     return -EOPNOTSUPP;
 }
 
+static inline unsigned long hvm_get_interrupt_shadow(struct vcpu *v)
+{
+    if ( hvm_funcs.get_interrupt_shadow )
+        return alternative_call(hvm_funcs.get_interrupt_shadow, v);
+
+    return -EOPNOTSUPP;
+}
+
+static inline void
+hvm_set_interrupt_shadow(struct vcpu *v, unsigned long val)
+{
+    if ( hvm_funcs.set_interrupt_shadow )
+        alternative_vcall(hvm_funcs.set_interrupt_shadow, v, val);
+}
+
+
 /*
  * Accessors for registers which have per-guest-type or per-vendor locations
  * (e.g. VMCS, msr load/save lists, VMCB, VMLOAD lazy, etc).
@@ -863,6 +879,16 @@ static inline void hvm_set_reg(struct vcpu *v, unsigned 
int reg, uint64_t val)
     ASSERT_UNREACHABLE();
 }
 
+static inline unsigned long hvm_get_interrupt_shadow(struct vcpu *v)
+{
+    ASSERT_UNREACHABLE();
+    return 0;
+}
+static inline void hvm_set_interrupt_shadow(struct vcpu *v, unsigned long val)
+{
+    ASSERT_UNREACHABLE();
+}
+
 #define is_viridian_domain(d) ((void)(d), false)
 #define is_viridian_vcpu(v) ((void)(v), false)
 #define has_viridian_time_ref_count(d) ((void)(d), false)
diff --git a/xen/include/public/arch-x86/hvm/save.h 
b/xen/include/public/arch-x86/hvm/save.h
index 773a380bc2..e944b1756a 100644
--- a/xen/include/public/arch-x86/hvm/save.h
+++ b/xen/include/public/arch-x86/hvm/save.h
@@ -165,7 +165,8 @@ struct hvm_hw_cpu {
 #define _XEN_X86_FPU_INITIALISED        0
 #define XEN_X86_FPU_INITIALISED         (1U<<_XEN_X86_FPU_INITIALISED)
     uint32_t flags;
-    uint32_t pad0;
+
+    uint32_t interruptibility_info;
 };
 
 struct hvm_hw_cpu_compat {
-- 
2.25.1