From: "Tian, Kevin" <kevin.tian@intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: "Zhao, Yan Y" <yan.y.zhao@intel.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
"jgg@nvidia.com" <jgg@nvidia.com>,
"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"luto@kernel.org" <luto@kernel.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>, "hpa@zytor.com" <hpa@zytor.com>,
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"will@kernel.org" <will@kernel.org>,
"robin.murphy@arm.com" <robin.murphy@arm.com>,
"baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>,
"Liu, Yi L" <yi.l.liu@intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>
Subject: RE: [PATCH 1/5] x86/pat: Let pat_pfn_immune_to_uc_mtrr() check MTRR for untracked PAT range
Date: Mon, 20 May 2024 02:36:20 +0000 [thread overview]
Message-ID: <BN9PR11MB5276FF52AD334D78F80985138CE92@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <ZkYTByuHu_IptChR@google.com>
> From: Sean Christopherson <seanjc@google.com>
> Sent: Thursday, May 16, 2024 10:07 PM
>
> +Tom
>
> On Thu, May 16, 2024, Kevin Tian wrote:
> > > From: Zhao, Yan Y <yan.y.zhao@intel.com>
> > > Sent: Tuesday, May 7, 2024 5:13 PM
> > >
> > > On Tue, May 07, 2024 at 04:26:37PM +0800, Tian, Kevin wrote:
> > > > > From: Zhao, Yan Y <yan.y.zhao@intel.com>
> > > > > Sent: Tuesday, May 7, 2024 2:19 PM
> > > > >
> > > > > @@ -705,7 +705,17 @@ static enum page_cache_mode
> > > > > lookup_memtype(u64 paddr)
> > > > > */
> > > > > bool pat_pfn_immune_to_uc_mtrr(unsigned long pfn)
> > > > > {
> > > > > - enum page_cache_mode cm =
> lookup_memtype(PFN_PHYS(pfn));
> > > > > + u64 paddr = PFN_PHYS(pfn);
> > > > > + enum page_cache_mode cm;
> > > > > +
> > > > > + /*
> > > > > + * Check MTRR type for untracked pat range since
> lookup_memtype()
> > > > > always
> > > > > + * returns WB for this range.
> > > > > + */
> > > > > + if (x86_platform.is_untracked_pat_range(paddr, paddr +
> PAGE_SIZE))
> > > > > + cm = pat_x_mtrr_type(paddr, paddr + PAGE_SIZE,
> > > > > _PAGE_CACHE_MODE_WB);
> > > >
> > > > doing so violates the name of this function. The PAT of the untracked
> > > > range is still WB and not immune to UC MTRR.
> > > Right.
> > > Do you think we can rename this function to something like
> > > pfn_of_uncachable_effective_memory_type() and make it work under
> > > !pat_enabled() too?
> >
> > let's hear from x86/kvm maintainers for their opinions.
> >
> > My gut-feeling is that kvm_is_mmio_pfn() might be moved into the
> > x86 core as the logic there has nothing specific to kvm itself. Also
> > naming-wise it doesn't really matter whether the pfn is mmio. The
> > real point is to find the uncacheble memtype in the primary mmu
> > and then follow it in KVM.
>
> Yeaaaah, we've got an existing problem there. When AMD's SME is enabled,
> KVM
> uses kvm_is_mmio_pfn() to determine whether or not to map memory into
> the guest
> as encrypted or plain text. I.e. KVM really does try to use this helper to
> detect MMIO vs. RAM. I highly doubt that actually works in all setups.
>
> For SME, it seems like the best approach would be grab the C-Bit from the
> host
> page tables, similar to how KVM uses host_pfn_mapping_level().
yes that sounds clearer. Checking MMIO vs. RAM is kind of indirect hint.
>
> SME aside, I don't have objection to moving kvm_is_mmio_pfn() out of KVM.
>
> > from that point probably a pfn_memtype_uncacheable() reads clearer.
>
> or even just pfn_is_memtype_uc()?
yes, better.
next prev parent reply other threads:[~2024-05-20 2:36 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-07 6:18 [PATCH 0/5] Enforce CPU cache flush for non-coherent device assignment Yan Zhao
2024-05-07 6:19 ` [PATCH 1/5] x86/pat: Let pat_pfn_immune_to_uc_mtrr() check MTRR for untracked PAT range Yan Zhao
2024-05-07 8:26 ` Tian, Kevin
2024-05-07 9:12 ` Yan Zhao
2024-05-08 22:14 ` Alex Williamson
2024-05-09 3:36 ` Yan Zhao
2024-05-16 7:42 ` Tian, Kevin
2024-05-16 14:07 ` Sean Christopherson
2024-05-20 2:36 ` Tian, Kevin [this message]
2024-05-07 6:20 ` [PATCH 2/5] KVM: x86/mmu: Fine-grained check of whether a invalid & RAM PFN is MMIO Yan Zhao
2024-05-07 8:39 ` Tian, Kevin
2024-05-07 9:19 ` Yan Zhao
2024-05-07 6:20 ` [PATCH 3/5] x86/mm: Introduce and export interface arch_clean_nonsnoop_dma() Yan Zhao
2024-05-07 8:51 ` Tian, Kevin
2024-05-07 9:40 ` Yan Zhao
2024-05-20 14:07 ` Christoph Hellwig
2024-05-21 15:49 ` Jason Gunthorpe
2024-05-21 16:00 ` Jason Gunthorpe
2024-05-22 3:41 ` Yan Zhao
2024-05-28 6:37 ` Christoph Hellwig
2024-06-01 19:46 ` Jason Gunthorpe
2024-06-06 2:48 ` Yan Zhao
2024-06-06 11:55 ` Jason Gunthorpe
2024-06-07 9:39 ` Yan Zhao
2024-05-07 6:21 ` [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in non-coherent domains Yan Zhao
2024-05-09 18:10 ` Alex Williamson
2024-05-10 10:31 ` Yan Zhao
2024-05-10 16:57 ` Alex Williamson
2024-05-13 7:11 ` Yan Zhao
2024-05-16 7:53 ` Tian, Kevin
2024-05-16 8:34 ` Tian, Kevin
2024-05-16 20:31 ` Alex Williamson
2024-05-17 17:11 ` Jason Gunthorpe
2024-05-20 2:52 ` Tian, Kevin
2024-05-21 16:07 ` Jason Gunthorpe
2024-05-21 16:21 ` Alex Williamson
2024-05-21 16:34 ` Jason Gunthorpe
2024-05-21 18:19 ` Alex Williamson
2024-05-21 18:37 ` Jason Gunthorpe
2024-05-22 6:24 ` Tian, Kevin
2024-05-22 12:29 ` Jason Gunthorpe
2024-05-22 14:43 ` Alex Williamson
2024-05-22 16:52 ` Jason Gunthorpe
2024-05-22 18:22 ` Alex Williamson
2024-05-22 23:26 ` Tian, Kevin
2024-05-22 23:32 ` Jason Gunthorpe
2024-05-22 23:40 ` Tian, Kevin
2024-05-23 14:58 ` Jason Gunthorpe
2024-05-23 22:47 ` Alex Williamson
2024-05-24 0:30 ` Tian, Kevin
2024-05-24 13:50 ` Jason Gunthorpe
2024-05-22 3:33 ` Yan Zhao
2024-05-22 3:24 ` Yan Zhao
2024-05-22 12:26 ` Jason Gunthorpe
2024-05-24 3:07 ` Yan Zhao
2024-05-16 20:50 ` Alex Williamson
2024-05-17 3:11 ` Yan Zhao
2024-05-17 4:44 ` Alex Williamson
2024-05-17 5:00 ` Yan Zhao
2024-05-07 6:22 ` [PATCH 5/5] iommufd: " Yan Zhao
2024-05-09 14:13 ` Jason Gunthorpe
2024-05-10 8:03 ` Yan Zhao
2024-05-10 13:29 ` Jason Gunthorpe
2024-05-13 7:43 ` Yan Zhao
2024-05-14 15:11 ` Jason Gunthorpe
2024-05-15 7:06 ` Yan Zhao
2024-05-15 20:43 ` Jason Gunthorpe
2024-05-16 2:32 ` Yan Zhao
2024-05-16 8:38 ` Tian, Kevin
2024-05-16 9:48 ` Yan Zhao
2024-05-17 17:04 ` Jason Gunthorpe
2024-05-20 2:45 ` Yan Zhao
2024-05-21 16:04 ` Jason Gunthorpe
2024-05-22 3:17 ` Yan Zhao
2024-05-22 6:29 ` Yan Zhao
2024-05-22 17:01 ` Jason Gunthorpe
2024-05-27 7:15 ` Yan Zhao
2024-06-01 16:48 ` Jason Gunthorpe
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