From: Alex Williamson <alex.williamson@redhat.com>
To: Yan Zhao <yan.y.zhao@intel.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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"Liu, Yi L" <yi.l.liu@intel.com>
Subject: Re: [PATCH 1/5] x86/pat: Let pat_pfn_immune_to_uc_mtrr() check MTRR for untracked PAT range
Date: Wed, 8 May 2024 16:14:24 -0600 [thread overview]
Message-ID: <20240508161424.5bf4bdfc.alex.williamson@redhat.com> (raw)
In-Reply-To: <ZjnwiKcmdpDAjMQ5@yzhao56-desk.sh.intel.com>
On Tue, 7 May 2024 17:12:40 +0800
Yan Zhao <yan.y.zhao@intel.com> wrote:
> 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
> > >
> > > However, lookup_memtype() defaults to returning WB for PFNs within the
> > > untracked PAT range, regardless of their actual MTRR type. This behavior
> > > could lead KVM to misclassify the PFN as non-MMIO, permitting cacheable
> > > guest access. Such access might result in MCE on certain platforms, (e.g.
> > > clflush on VGA range (0xA0000-0xBFFFF) triggers MCE on some platforms).
> >
> > the VGA range is not exposed to any guest today. So is it just trying to
> > fix a theoretical problem?
>
> Yes. Not sure if VGA range is allowed to be exposed to guest in future, given
> we have VFIO variant drivers.
include/uapi/linux/vfio.h:
/*
* Expose VGA regions defined for PCI base class 03, subclass 00.
* This includes I/O port ranges 0x3b0 to 0x3bb and 0x3c0 to 0x3df
* as well as the MMIO range 0xa0000 to 0xbffff. Each implemented
* range is found at it's identity mapped offset from the region
* offset, for example 0x3b0 is region_info.offset + 0x3b0. Areas
* between described ranges are unimplemented.
*/
VFIO_PCI_VGA_REGION_INDEX,
We don't currently support mmap for this region though, so I think we
still don't technically require this, but I guess an mmap through KVM
is theoretically possible. Thanks,
Alex
> > > @@ -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?
>
> >
> > > + else
> > > + cm = lookup_memtype(paddr);
> > >
> > > return cm == _PAGE_CACHE_MODE_UC ||
> > > cm == _PAGE_CACHE_MODE_UC_MINUS ||
> >
>
next prev parent reply other threads:[~2024-05-08 22:14 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 [this message]
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
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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