Re: [PATCH] simplify pdpte check

[Muli Ben-Yehuda <muli-7z/5BgaJwgfQT0dZR+AlfA@public.gmane.org>]

On Thu, Feb 01, 2007 at 04:07:01PM +0200, Avi Kivity wrote:
> Muli Ben-Yehuda wrote:
> >Small cleanup: we check (pdpte & 1) && (pdpte & constant). Instead
> >just check (pdpte & (constant | 1)).
> >
> >Signed-off-by: Muli Ben-Yehuda <muli-7z/5BgaJwgfQT0dZR+AlfA@public.gmane.org>
> >
> >Index: kernel/kvm_main.c
> >===================================================================
> >--- kernel/kvm_main.c	(revision 4379)
> >+++ kernel/kvm_main.c	(working copy)
> >@@ -336,7 +336,7 @@
> > 	ret = 1;
> > 	for (i = 0; i < 4; ++i) {
> > 		pdpte = pdpt[offset + i];
> >-		if ((pdpte & 1) && (pdpte & 0xfffffff0000001e6ull)) {
> >+		if (pdpte & 0xfffffff0000001e7ull) {
> > 			ret = 0;
> > 			goto out;
> > 		}
> >
> >  
> 
> The code is not equivalent.  For example, pdpte == 2 passes the check 
> before the patch and fails it after.

err... 2 & 1 == 0, which does not pass the original check. Perhaps the
real error is '&&' instead of '||' in the original conditional?

Cheers,
Muli

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