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Date: Wed, 13 Jul 2016 11:06:50 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Bandan Das <bsd@...hat.com>, kvm@...r.kernel.org Cc: guangrong.xiao@...ux.intel.com, kernellwp@...il.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 4/5] mmu: change unconditional setting of the u bit in fault bitmap On 13/07/2016 10:23, Paolo Bonzini wrote: > > > 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 <bsd@...hat.com> >> --- >> 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; ... in fact I think this should be removed completely. If shadow_present_mask is set, the R bit will always be set in a present PTE and FNAME(gpte_access) will change that to ACC_USER_MASK---which in turn means that u=1. Paolo >> + } >> >> 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 >
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