[Xen-devel] [PATCH for-4.11 v2 1/3] x86/HVM: don't cause #NM to be raised in Xen

["Jan Beulich" <JBeulich@xxxxxxxx>]

The changes for XSA-267 did not touch management of CR0.TS for HVM
guests. In fully eager mode this bit should never be set when
respective vCPU-s are active, or else hvmemul_get_fpu() might leave it
wrongly set, leading to #NM in hypervisor context.

{svm,vmx}_enter() and {svm,vmx}_fpu_dirty_intercept() become unreachable
this way. Explicit {svm,vmx}_fpu_leave() invocations need to be guarded
now.

With no CR0.TS management necessary in fully eager mode, there's also no
need anymore to intercept #NM.

Reported-by: Charles Arnold <carnold@xxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Correct host_cr0 calculation in construct_vmcs().
---
TBD: A few ASSERT()s could be sprinkled around, but I wasn't sure how
     far to go with this, so I've left them out altogether for now.

--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -574,7 +574,10 @@ void svm_update_guest_cr(struct vcpu *v,
         if ( !(v->arch.hvm_vcpu.guest_cr[0] & X86_CR0_TS) )
         {
             if ( v != current )
-                hw_cr0_mask |= X86_CR0_TS;
+            {
+                if ( !v->arch.fully_eager_fpu )
+                    hw_cr0_mask |= X86_CR0_TS;
+            }
             else if ( vmcb_get_cr0(vmcb) & X86_CR0_TS )
                 svm_fpu_enter(v);
         }
@@ -1083,7 +1086,8 @@ static void svm_ctxt_switch_from(struct
     if ( unlikely((read_efer() & EFER_SVME) == 0) )
         return;
 
-    svm_fpu_leave(v);
+    if ( !v->arch.fully_eager_fpu )
+        svm_fpu_leave(v);
 
     svm_save_dr(v);
     svm_lwp_save(v);
--- a/xen/arch/x86/hvm/svm/vmcb.c
+++ b/xen/arch/x86/hvm/svm/vmcb.c
@@ -180,8 +180,8 @@ static int construct_vmcb(struct vcpu *v
     paging_update_paging_modes(v);
 
     vmcb->_exception_intercepts =
-        HVM_TRAP_MASK
-        | (1U << TRAP_no_device);
+        HVM_TRAP_MASK |
+        (v->arch.fully_eager_fpu ? 0 : (1U << TRAP_no_device));
 
     if ( paging_mode_hap(v->domain) )
     {
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1144,7 +1144,9 @@ static int construct_vmcs(struct vcpu *v
     __vmwrite(HOST_TR_SELECTOR, TSS_ENTRY << 3);
 
     /* Host control registers. */
-    v->arch.hvm_vmx.host_cr0 = read_cr0() | X86_CR0_TS;
+    v->arch.hvm_vmx.host_cr0 = read_cr0() & ~X86_CR0_TS;
+    if ( !v->arch.fully_eager_fpu )
+        v->arch.hvm_vmx.host_cr0 |= X86_CR0_TS;
     __vmwrite(HOST_CR0, v->arch.hvm_vmx.host_cr0);
     __vmwrite(HOST_CR4, mmu_cr4_features);
 
@@ -1223,7 +1225,7 @@ static int construct_vmcs(struct vcpu *v
 
     v->arch.hvm_vmx.exception_bitmap = HVM_TRAP_MASK
               | (paging_mode_hap(d) ? 0 : (1U << TRAP_page_fault))
-              | (1U << TRAP_no_device);
+              | (v->arch.fully_eager_fpu ? 0 : (1U << TRAP_no_device));
     vmx_update_exception_bitmap(v);
 
     v->arch.hvm_vcpu.guest_cr[0] = X86_CR0_PE | X86_CR0_ET;
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -936,7 +936,8 @@ static void vmx_ctxt_switch_from(struct
         vmx_vmcs_reload(v);
     }
 
-    vmx_fpu_leave(v);
+    if ( !v->arch.fully_eager_fpu )
+        vmx_fpu_leave(v);
     vmx_save_guest_msrs(v);
     vmx_restore_host_msrs();
     vmx_save_dr(v);
@@ -1493,7 +1494,10 @@ static void vmx_update_guest_cr(struct v
         if ( !(v->arch.hvm_vcpu.guest_cr[0] & X86_CR0_TS) )
         {
             if ( v != current )
-                hw_cr0_mask |= X86_CR0_TS;
+            {
+                if ( !v->arch.fully_eager_fpu )
+                    hw_cr0_mask |= X86_CR0_TS;
+            }
             else if ( v->arch.hvm_vcpu.hw_cr[0] & X86_CR0_TS )
                 vmx_fpu_enter(v);
         }





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