From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Subject: Re: [PATCH 1/4] KVM: MMU: correct the behavior of mmu_spte_update_no_track Date: Thu, 17 Jan 2019 07:44:54 -0800 Message-ID: <20190117154454.GA22169@linux.intel.com> References: <1547733331-16140-1-git-send-email-ann.zhuangyanying@huawei.com> <1547733331-16140-2-git-send-email-ann.zhuangyanying@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: liu.jinsong@huawei.com, kvm@vger.kernel.org, wangxinxin.wang@huawei.com, xiaoguangrong@tencent.com, qemu-devel@nongnu.org, arei.gonglei@huawei.com, pbonzini@redhat.com To: Zhuangyanying Return-path: Content-Disposition: inline In-Reply-To: <1547733331-16140-2-git-send-email-ann.zhuangyanying@huawei.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org On Thu, Jan 17, 2019 at 01:55:28PM +0000, Zhuangyanying wrote: > From: Xiao Guangrong > > Current behavior of mmu_spte_update_no_track() does not match > the name of _no_track() as actually the A/D bits are tracked > and returned to the caller Sentences should be terminated with periods. > This patch introduces the real _no_track() function to update "This patch" is redundant, e.g. simply state "Introduce ...". > the spte regardless of A/D bits and rename the original function > to _track() The function also avoids __update_clear_spte_slow(), i.e. AFAICT it doesn't guarantee volatile bits will be preserved. I assume this is intentional, but it'd be nice to explain why this is ok. > The _no_track() function will be used by later patches to update > upper spte which need not care of A/D bits indeed The _no_track() variant is already used (by mmu_spte_age()), I don't see any point in having this blurb on the changelog, e.g. it led me to incorrectly think an unused function was being introduced. > Signed-off-by: Xiao Guangrong > --- > arch/x86/kvm/mmu.c | 25 ++++++++++++++++++++++--- > 1 file changed, 22 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index ce770b4..eeb3bac 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -731,10 +731,29 @@ static void mmu_spte_set(u64 *sptep, u64 new_spte) > } > > /* > - * Update the SPTE (excluding the PFN), but do not track changes in its > + * Update the SPTE (excluding the PFN) regardless of accessed/dirty > + * status which is used to update the upper level spte. > + */ > +static void mmu_spte_update_no_track(u64 *sptep, u64 new_spte) > +{ > + u64 old_spte = *sptep; No need to snapshot the old spte since it's not being returned. > + WARN_ON(!is_shadow_present_pte(new_spte)); > + > + if (!is_shadow_present_pte(old_spte)) { > + mmu_spte_set(sptep, new_spte); > + return; Similarly, this is more complex than it needs to be, e.g. the function can be simplified to: static void mmu_spte_update_no_track(u64 *sptep, u64 new_spte) { WARN_ON(!is_shadow_present_pte(new_spte)); if (!is_shadow_present_pte(*sptep)) mmu_spte_set(sptep, new_spte); else __update_clear_spte_fast(sptep, new_spte); } > + } > + > + __update_clear_spte_fast(sptep, new_spte); > +} > + > +/* > + * Update the SPTE (excluding the PFN), the original value is > + * returned, based on it, the caller can track changes of its > * accessed/dirty status. > */ > -static u64 mmu_spte_update_no_track(u64 *sptep, u64 new_spte) > +static u64 mmu_spte_update_track(u64 *sptep, u64 new_spte) > { > u64 old_spte = *sptep; > > @@ -769,7 +788,7 @@ static u64 mmu_spte_update_no_track(u64 *sptep, u64 new_spte) > static bool mmu_spte_update(u64 *sptep, u64 new_spte) > { > bool flush = false; > - u64 old_spte = mmu_spte_update_no_track(sptep, new_spte); > + u64 old_spte = mmu_spte_update_track(sptep, new_spte); > > if (!is_shadow_present_pte(old_spte)) > return false; > -- > 1.8.3.1 > >