Messages in this thread | | | Date | Wed, 30 Apr 2014 13:41:20 +0100 | From | David Vrabel <> | Subject | Re: [PATCH 7/9] x86: skip check for spurious faults for non-present faults |
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On 15/04/14 15:15, David Vrabel wrote: > If a fault on a kernel address is due to a non-present page, then it > cannot be the result of stale TLB entry from a protection change (RO > to RW or NX to X). Thus the pagetable walk in spurious_fault() can be > skipped. > > This avoids spurious_fault() oopsing in some cases if the pagetables > it attempts to walk are not accessible. This obscures the location of > the original fault. > > This also fixes a crash with Xen PV guests when they access entries in > the M2P corresponding to device MMIO regions. The M2P is mapped > (read-only) by Xen into the kernel address space of the guest and this > mapping may contains holes for non-RAM regions. Read faults will > result in calls to spurious_fault(), but because the page tables for > the M2P mappings are not accessible by the guest the pagetable walk > would fault. > > This was not normally a problem as MMIO mappings would not normally > result in a M2P lookup because of the use of the _PAGE_IOMAP bit the > PTE. However, removing the _PAGE_IOMAP bit requires M2P lookups for > MMIO mappings as well. > > Signed-off-by: David Vrabel <david.vrabel@citrix.com> > Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > --- > x86 maintainers, this is a prerequisite for removing Xen's usage of > _PAGE_IOMAP so I think this is best merged via the Xen tree.
Peter, any opinion on this patch?
David
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