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    SubjectRe: [PATCH 4/4] Enabling Access bit when doing memory swapping
    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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