Messages in this thread | | | Date | Mon, 21 May 2012 14:31:14 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 4/4] Enabling Access bit when doing memory swapping |
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On 05/21/2012 02:17 PM, Hao, Xudong wrote: > > -----Original Message----- > > From: Avi Kivity [mailto:avi@redhat.com] > > Sent: Monday, May 21, 2012 6:48 PM > > To: Hao, Xudong > > Cc: Marcelo Tosatti; Xudong Hao; kvm@vger.kernel.org; > > linux-kernel@vger.kernel.org; Shan, Haitao; Zhang, Xiantao > > Subject: Re: [PATCH 4/4] Enabling Access bit when doing memory swapping > > > > On 05/21/2012 01:35 PM, Hao, Xudong wrote: > > > > > > > > That doesn't answer the question. An atomic operation is now > > non-atomic. > > > > > > > > You can calculate shadow_accessed_bit and keep on using clear_bit(), or > > > > switch to cmpxchg64(), but don't just drop the dirty bit here. > > > > > > > > > > I know your meaning. How about this changes: > > > > > > ... > > > young = 1; > > > + if (enable_ept_ad_bits) > > > + clear_bit(ffs(shadow_accessed_mask), (unsigned long > > *)spte); > > > > ffs() returns an off-by-one result, so this needs to be adjusted. > > Yes, it need to decrease 1, I'll send v3 version for patch4, any other comments?
I think it's fine.
> > IIRC > > bsfl is slow, but this shouldn't be a problem here. > > > > I do not know the story... >
No story, bsf is a relatively slow instruction, but it shouldn't affect us here; this isn't a fast path and in any case it's only a few cycles.
-- error compiling committee.c: too many arguments to function
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