From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bandan Das Subject: Re: [PATCH 1/5] mmu: mark spte present if the x bit is set Date: Tue, 28 Jun 2016 17:04:17 -0400 Message-ID: References: <1467088360-10186-1-git-send-email-bsd@redhat.com> <1467088360-10186-2-git-send-email-bsd@redhat.com> <55601232-c941-74e8-f740-fd09e9e8a6ae@redhat.com> <70de38d1-2743-09dd-dc47-6242799a701c@redhat.com> Mime-Version: 1.0 Content-Type: text/plain Cc: kvm@vger.kernel.org, guangrong.xiao@linux.intel.com, linux-kernel@vger.kernel.org To: Paolo Bonzini Return-path: In-Reply-To: <70de38d1-2743-09dd-dc47-6242799a701c@redhat.com> (Paolo Bonzini's message of "Tue, 28 Jun 2016 22:49:17 +0200") Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Paolo Bonzini writes: > On 28/06/2016 22:37, Bandan Das wrote: >> Paolo Bonzini writes: >> >>> On 28/06/2016 19:33, Bandan Das wrote: >>>>>>>> static int is_shadow_present_pte(u64 pte) >>>>>>>> { >>>>>>>> - return pte & PT_PRESENT_MASK && !is_mmio_spte(pte); >>>>>>>> + return pte & (PT_PRESENT_MASK | shadow_x_mask) && >>>>>>>> + !is_mmio_spte(pte); >>>>>> >>>>>> This should really be pte & 7 when using EPT. But this is okay as an >>>>>> alternative to a new shadow_present_mask. >>>> I could revive shadow_xonly_valid probably... Anyway, for now I will >>>> add a TODO comment here. >>> >>> It's okay to it like this, because the only invalid PTEs reaching this >>> point are those that is_mmio_spte filters away. Hence you'll never get >>> -W- PTEs here, and pte & 7 is really the same as how you wrote it. It's >>> pretty clever, and doesn't need a TODO at all. :) >> >> Thanks, understood. So, the way it is written now covers all cases for >> pte & 7. Let's still add a comment - clever things are usually >> confusing to many! > > I think another way to write it is "(pte & 0xFFFFFFFFull) && > !is_mmio_spte(pte)", since non-present/non-MMIO SPTEs never use bits > 1..31 (they can have non-zero bits 32..63 on 32-bit CPUs where we don't > update the PTEs atomically). Guangrong, what do you prefer? Actually, I like this one better although until now, I was not sure if it's a safe assumption for non-ept cases. From your description, it looks like it is. > Paolo