Re: [Xen-devel] [PATCH v3 5/9] x86/vvmx: make updating shadow EPTP value more efficient

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

On Thu, 2017-10-05 at 03:27 -0600, Jan Beulich wrote:
> > > > On 05.10.17 at 10:18, <sergey.dyasli@xxxxxxxxxx> wrote:
> > 
> > --- a/xen/arch/x86/hvm/vmx/entry.S
> > +++ b/xen/arch/x86/hvm/vmx/entry.S
> > @@ -80,7 +80,7 @@ UNLIKELY_END(realmode)
> >          mov  %rsp,%rdi
> >          call vmx_vmenter_helper
> >          cmp  $0,%eax
> > -        jne .Lvmx_vmentry_restart
> > +        je .Lvmx_vmentry_restart
> 
> If you make the function return bool, the cmp above also needs
> changing (and then preferably to "test %al, %al", in which case
> it would then also better be "jz" instead of "je").

Here's the updated delta:

diff --git a/xen/arch/x86/hvm/vmx/entry.S b/xen/arch/x86/hvm/vmx/entry.S
index 9fb8f89220..47cd674260 100644
--- a/xen/arch/x86/hvm/vmx/entry.S
+++ b/xen/arch/x86/hvm/vmx/entry.S
@@ -79,8 +79,8 @@ UNLIKELY_END(realmode)
 
         mov  %rsp,%rdi
         call vmx_vmenter_helper
-        cmp  $0,%eax
-        jne .Lvmx_vmentry_restart
+        test %al, %al
+        jz .Lvmx_vmentry_restart
         mov  VCPU_hvm_guest_cr2(%rbx),%rax
 
         pop  %r15
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index c9a4111267..a5c2bd71cd 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -4197,7 +4197,8 @@ static void lbr_fixup(void)
         bdw_erratum_bdf14_fixup();
 }
 
-int vmx_vmenter_helper(const struct cpu_user_regs *regs)
+/* Returns false if the vmentry has to be restarted */
+bool vmx_vmenter_helper(const struct cpu_user_regs *regs)
 {
     struct vcpu *curr = current;
     u32 new_asid, old_asid;
@@ -4206,7 +4207,7 @@ int vmx_vmenter_helper(const struct cpu_user_regs *regs)
 
     /* Shadow EPTP can't be updated here because irqs are disabled */
      if ( nestedhvm_vcpu_in_guestmode(curr) && vcpu_nestedhvm(curr).stale_np2m 
)
-         return 1;
+         return false;
 
     if ( curr->domain->arch.hvm_domain.pi_ops.do_resume )
         curr->domain->arch.hvm_domain.pi_ops.do_resume(curr);
@@ -4269,7 +4270,7 @@ int vmx_vmenter_helper(const struct cpu_user_regs *regs)
     __vmwrite(GUEST_RSP,    regs->rsp);
     __vmwrite(GUEST_RFLAGS, regs->rflags | X86_EFLAGS_MBS);
 
-    return 0;
+    return true;
 }
 
 /*

-- 
Thanks,
Sergey
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