On 05/21/2012 06:22 AM, Hao, Xudong wrote: > > -----Original Message----- > > From: Marcelo Tosatti [mailto:mtosatti@xxxxxxxxxx] > > Sent: Friday, May 18, 2012 10:23 AM > > To: Xudong Hao > > Cc: avi@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > Shan, Haitao; Zhang, Xiantao; Hao, Xudong > > Subject: Re: [PATCH 4/4] Enabling Access bit when doing memory swapping > > > > On Wed, May 16, 2012 at 09:12:30AM +0800, Xudong Hao wrote: > > > Enabling Access bit when doing memory swapping. > > > > > > Signed-off-by: Haitao Shan <haitao.shan@xxxxxxxxx> > > > Signed-off-by: Xudong Hao <xudong.hao@xxxxxxxxx> > > > --- > > > arch/x86/kvm/mmu.c | 13 +++++++------ > > > arch/x86/kvm/vmx.c | 6 ++++-- > > > 2 files changed, 11 insertions(+), 8 deletions(-) > > > > > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > > > index ff053ca..5f55f98 100644 > > > --- a/arch/x86/kvm/mmu.c > > > +++ b/arch/x86/kvm/mmu.c > > > @@ -1166,7 +1166,8 @@ static int kvm_age_rmapp(struct kvm *kvm, > > unsigned long *rmapp, > > > int young = 0; > > > > > > /* > > > - * Emulate the accessed bit for EPT, by checking if this page has > > > + * In case of absence of EPT Access and Dirty Bits supports, > > > + * emulate the accessed bit for EPT, by checking if this page has > > > * an EPT mapping, and clearing it if it does. On the next access, > > > * a new EPT mapping will be established. > > > * This has some overhead, but not as much as the cost of swapping > > > @@ -1179,11 +1180,11 @@ static int kvm_age_rmapp(struct kvm *kvm, > > unsigned long *rmapp, > > > while (spte) { > > > int _young; > > > u64 _spte = *spte; > > > - BUG_ON(!(_spte & PT_PRESENT_MASK)); > > > - _young = _spte & PT_ACCESSED_MASK; > > > + BUG_ON(!is_shadow_present_pte(_spte)); > > > + _young = _spte & shadow_accessed_mask; > > > if (_young) { > > > young = 1; > > > - clear_bit(PT_ACCESSED_SHIFT, (unsigned long *)spte); > > > + *spte &= ~shadow_accessed_mask; > > > } > > > > Now a dirty bit can be lost. Is there a reason to remove the clear_bit? > > The clear_bit() is called in shadown and EPT A/D mode, because PT_ACCESSED_SHIFT does not make sense for EPT A/D bit, so use the code shadow_accessed_mask to mask the bit for both of them. 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. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
