[Xen-devel] [PATCH] SVM: limit GIF=0 region

["Jan Beulich" <JBeulich@xxxxxxxx>]

Use EFLAGS.IF for all ordinary purposes; there's in particular no need
to unduly defer NMI/#MC. Clear/set GIF solely around VMRUN itself. This
has the additional advantage that svm_stgi_label now indeed marks the
only place where GIF is being set.

A note regarding the main STI placement: Orignally I had it at the place
the main STGI was sitting at so far. However, my Fam15 box reliably
locks up hard with this, unless I have the NMI watchdog enabled. I can
only deduce that the CPU doesn't like STGI with EFLAGS.IF clear plus
some other condition (the lockup occurs only after exiting the boot
loader in the guest). As there's nothing wrong with interrupts being on
right after VMRUN, I've decided to put the STI right after the CLGI
(matching what KVM does, i.e. having a fair chance of working
everywhere).

Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/svm/entry.S
+++ b/xen/arch/x86/hvm/svm/entry.S
@@ -43,7 +43,7 @@ ENTRY(svm_asm_do_resume)
         lea  irq_stat+IRQSTAT_softirq_pending(%rip),%rdx
         xor  %ecx,%ecx
         shl  $IRQSTAT_shift,%eax
-        CLGI
+        cli
         cmp  %ecx,(%rdx,%rax,1)
         jne  .Lsvm_process_softirqs
 
@@ -57,7 +57,7 @@ UNLIKELY_START(ne, nsvm_hap)
          * Someone shot down our nested p2m table; go round again
          * and nsvm_vcpu_switch() will fix it for us.
          */
-        STGI
+        sti
         jmp  .Lsvm_do_resume
 __UNLIKELY_END(nsvm_hap)
 
@@ -87,7 +87,11 @@ __UNLIKELY_END(nsvm_hap)
         pop  %rsi
         pop  %rdi
 
+        CLGI
+        sti
         VMRUN
+        STGI
+GLOBAL(svm_stgi_label)
 
         SAVE_ALL
 
@@ -96,13 +100,11 @@ __UNLIKELY_END(nsvm_hap)
         SPEC_CTRL_ENTRY_FROM_HVM    /* Req: b=curr %rsp=regs/cpuinfo, Clob: 
acd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
-        STGI
-GLOBAL(svm_stgi_label)
         mov  %rsp,%rdi
         call svm_vmexit_handler
         jmp  .Lsvm_do_resume
 
 .Lsvm_process_softirqs:
-        STGI
+        sti
         call do_softirq
         jmp  .Lsvm_do_resume





_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel