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Date: Sun, 13 May 2018 16:25:58 +0800 From: Wanpeng Li <kernellwp@...il.com> To: Liran Alon <liran.alon@...cle.com> Cc: Radim Krcmar <rkrcmar@...hat.com>, Paolo Bonzini <pbonzini@...hat.com>, LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>, Junaid Shahid <junaids@...gle.com> Subject: Re: [PATCH 1/2] KVM: X86: Fix CR3 reserve bits 2018-05-13 15:53 GMT+08:00 Liran Alon <liran.alon@...cle.com>: > > ----- kernellwp@...il.com wrote: > >> From: Wanpeng Li <wanpengli@...cent.com> >> >> MSB of CR3 is a reserved bit if the PCIDE bit is not set in CR4. >> It should be checked when PCIDE bit is not set, however commit >> 'd1cd3ce900441 ("KVM: MMU: check guest CR3 reserved bits based on >> its physical address width")' removes the bit 63 checking >> unconditionally. This patch fixes it by checking bit 63 of CR3 >> when PCIDE bit is not set in CR4. >> >> Fixes: d1cd3ce900441 (KVM: MMU: check guest CR3 reserved bits based on >> its physical address width) >> Cc: Paolo Bonzini <pbonzini@...hat.com> >> Cc: Radim Krčmář <rkrcmar@...hat.com> >> Cc: Junaid Shahid <junaids@...gle.com> >> Signed-off-by: Wanpeng Li <wanpengli@...cent.com> >> --- >> arch/x86/kvm/emulate.c | 4 +++- >> arch/x86/kvm/x86.c | 2 +- >> 2 files changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c >> index b3705ae..b21f427 100644 >> --- a/arch/x86/kvm/emulate.c >> +++ b/arch/x86/kvm/emulate.c >> @@ -4189,7 +4189,9 @@ static int check_cr_write(struct >> x86_emulate_ctxt *ctxt) >> maxphyaddr = eax & 0xff; >> else >> maxphyaddr = 36; >> - rsvd = rsvd_bits(maxphyaddr, 62); >> + if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE) >> + new_val &= ~CR3_PCID_INVD; >> + rsvd = rsvd_bits(maxphyaddr, 63); > > I would prefer instead to do this: > if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE) > rsvd &= ~CR3_PCID_INVD; > It makes more sense as opposed to temporary removing the CR3_PCID_INVD bit from new_val. It tries the same way https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c19986fea873f3c745122bf79013a872a190f212 pointed out. Regards, Wanpeng Li > >> } >> >> if (new_val & rsvd) >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 87e4805..9a90668 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -863,7 +863,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned >> long cr3) >> } >> >> if (is_long_mode(vcpu) && >> - (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 62))) >> + (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63))) >> return 1; >> else if (is_pae(vcpu) && is_paging(vcpu) && >> !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3)) >> -- >> 2.7.4
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