From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v2 4/5] mmu: change unconditional setting of the u bit in fault bitmap Date: Wed, 13 Jul 2016 10:23:41 +0200 Message-ID: <2ef821e8-fa03-8797-fe05-261d30dcee28@redhat.com> References: <1468361932-16580-1-git-send-email-bsd@redhat.com> <1468361932-16580-5-git-send-email-bsd@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: guangrong.xiao@linux.intel.com, kernellwp@gmail.com, linux-kernel@vger.kernel.org To: Bandan Das , kvm@vger.kernel.org Return-path: In-Reply-To: <1468361932-16580-5-git-send-email-bsd@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 13/07/2016 00:18, Bandan Das wrote: > For the nested EPT case, we assume that the read bit (u) is > always set since we used to unconditionally set it in set_spte(). > Modify it to only be set when host ept execute only support > isn't present. > > Signed-off-by: Bandan Das > --- > arch/x86/kvm/mmu.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index c364dcb..566eea5 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -3923,9 +3923,10 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, > * clearer. > */ > smap = cr4_smap && u && !uf && !ff; > - } else > - /* Not really needed: no U/S accesses on ept */ > - u = 1; > + } else { > + if (shadow_present_mask) > + u = 1; > + } > > fault = (ff && !x) || (uf && !u) || (wf && !w) || > (smapf && smap); > This is needed too, in order to look up with the correct uf: diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 003618e324ce..941d345ebd2c 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6014,12 +6014,14 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu) gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS); trace_kvm_page_fault(gpa, exit_qualification); - /* It is a write fault? */ + /* it is a read fault? */ + error_code = (exit_qualification << 2) & PFERR_USER_MASK; + /* it is a write fault? */ error_code = exit_qualification & PFERR_WRITE_MASK; /* It is a fetch fault? */ error_code |= (exit_qualification << 2) & PFERR_FETCH_MASK; /* ept page table is present? */ - error_code |= (exit_qualification >> 3) & PFERR_PRESENT_MASK; + error_code |= (exit_qualification & 0x38) != 0; vcpu->arch.exit_qualification = exit_qualification; Otherwise you always lookup the permission bitmap for an uf=0 case. This was the meaning of the "Not really needed" comment. Paolo