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Peter Anvin" , x86@kernel.org, Borislav Petkov , linux-kernel@vger.kernel.org, Dave Hansen , Thomas Gleixner Date: Wed, 24 Jul 2024 14:18:21 -0400 In-Reply-To: References: <20240716022014.240960-1-mlevitsk@redhat.com> <20240716022014.240960-2-mlevitsk@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7bit On Tue, 2024-07-16 at 14:07 -0700, Sean Christopherson wrote: > On Mon, Jul 15, 2024, Maxim Levitsky wrote: > > In prepare_vmcs02_rare, call vmx_segment_cache_clear, instead > > of setting the segment_cache.bitmask directly. > > > > No functional change intended. > > > > Signed-off-by: Maxim Levitsky > > --- > > arch/x86/kvm/vmx/nested.c | 5 +++-- > > arch/x86/kvm/vmx/vmx.c | 4 ---- > > arch/x86/kvm/vmx/vmx.h | 5 +++++ > > 3 files changed, 8 insertions(+), 6 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > > index 643935a0f70ab..d3ca1a772ae67 100644 > > --- a/arch/x86/kvm/vmx/nested.c > > +++ b/arch/x86/kvm/vmx/nested.c > > @@ -2469,6 +2469,9 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12) > > > > if (!hv_evmcs || !(hv_evmcs->hv_clean_fields & > > HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP2)) { > > + > > + vmx_segment_cache_clear(vmx); > > + > > vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector); > > vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector); > > vmcs_write16(GUEST_SS_SELECTOR, vmcs12->guest_ss_selector); > > @@ -2505,8 +2508,6 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12) > > vmcs_writel(GUEST_TR_BASE, vmcs12->guest_tr_base); > > vmcs_writel(GUEST_GDTR_BASE, vmcs12->guest_gdtr_base); > > vmcs_writel(GUEST_IDTR_BASE, vmcs12->guest_idtr_base); > > - > > - vmx->segment_cache.bitmask = 0; > > This actually exacerbates the bug that you're trying fix in patch 2. Clearing > segment_cache.bitmask _after_ writing the relevant state limits the stale data > to only the accessor that's running in IRQ context (kvm_arch_vcpu_put()). > > Clearing segment_cache.bitmask _before_ writing the relevant statement means > that kvm_arch_vcpu_put() _and_ all future readers will be exposed to the stale > data, because the stale data cached by kvm_arch_vcpu_put() won't mark it invalid. > I noticed that after I sent the patch series, this makes sense. Best regards, Maxim Levitsky