From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH] No need to emulate WBINVD when VT-d force snooping feature available Date: Mon, 5 Jul 2010 11:09:55 +0100 Message-ID: References: <4FA716B1526C7C4DB0375C6DADBC4EA37ACFC7A310@LONPMAILBOX01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4FA716B1526C7C4DB0375C6DADBC4EA37ACFC7A310@LONPMAILBOX01.citrite.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Pratt , Sheng Yang Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 05/07/2010 10:36, "Ian Pratt" wrote: >> There is no cache coherency issue if VT-d engine's force snooping feature >> available. > > Isn't it also necessary to explicitly set the SNP bit in each VTd PTE to force > snooping? I don't believe we do this today, but since we ignore guest PAT > settings on RAM we should do so. In drivers/passthrough/vtd/iommu.c:intel_iommu_map_page() --- /* Set the SNP on leaf page table if Snoop Control available */ if ( iommu_snoop ) dma_set_pte_snp(*pte); -- Keir > Thanks, > Ian > > >> Signed-off-by: Sheng Yang >> >> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c >> --- a/xen/arch/x86/hvm/vmx/vmcs.c >> +++ b/xen/arch/x86/hvm/vmx/vmcs.c >> @@ -1064,8 +1064,10 @@ >> * 1: flushing cache (wbinvd) when the guest is scheduled out if >> * there is no wbinvd exit, or >> * 2: execute wbinvd on all dirty pCPUs when guest wbinvd exits. >> + * If VT-d engine can force snooping, we don't need to do these. >> */ >> - if ( has_arch_pdevs(v->domain) && !cpu_has_wbinvd_exiting ) >> + if ( has_arch_pdevs(v->domain) && !iommu_snoop >> + && !cpu_has_wbinvd_exiting ) >> { >> int cpu = v->arch.hvm_vmx.active_cpu; >> if ( cpu != -1 ) >> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c >> --- a/xen/arch/x86/hvm/vmx/vmx.c >> +++ b/xen/arch/x86/hvm/vmx/vmx.c >> @@ -2089,6 +2089,9 @@ >> if ( !has_arch_mmios(current->domain) ) >> return; >> >> + if ( iommu_snoop ) >> + return; >> + >> if ( cpu_has_wbinvd_exiting ) >> on_each_cpu(wbinvd_ipi, NULL, 1); >> else