Re: [Xen-devel] [PATCH] x86/p2m-ept: Don't unmap the EPT pagetable while it is still in use

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/30/2015 06:09 PM, Andrew Cooper wrote:
> The call to iommu_pte_flush() between the two hunks uses &ept_entry->epte
> which is a pointer into the mapped page.
> 
> It is eventually passed to `clflush` instruction which will suffer a pagefault
> if the virtual mapping has fallen out of the TLB.
> 
>     (XEN) ----[ Xen-4.5.0-xs102594-d  x86_64  debug=y  Not tainted ]----
>     (XEN) CPU:    7
>     (XEN) RIP:    e008:[<ffff82d0801572f0>] cacheline_flush+0x4/0x9
>     <snip>
>     (XEN) Xen call trace:
>     (XEN)    [<ffff82d0801572f0>] cacheline_flush+0x4/0x9
>     (XEN)    [<ffff82d08014ffff>] __iommu_flush_cache+0x4a/0x6a
>     (XEN)    [<ffff82d0801532e2>] iommu_pte_flush+0x2b/0xd5
>     (XEN)    [<ffff82d0801f909a>] ept_set_entry+0x4bc/0x61f
>     (XEN)    [<ffff82d0801f0c25>] p2m_set_entry+0xd1/0x112
>     (XEN)    [<ffff82d0801f25b1>] clear_mmio_p2m_entry+0x1a0/0x200
>     (XEN)    [<ffff82d0801f4aac>] unmap_mmio_regions+0x49/0x73
>     (XEN)    [<ffff82d080106292>] do_domctl+0x15bd/0x1edb
>     (XEN)    [<ffff82d080234fcb>] syscall_enter+0xeb/0x145
>     (XEN)
>     (XEN) Pagetable walk from ffff820040004ae0:
>     (XEN)  L4[0x104] = 00000008668a5063 ffffffffffffffff
>     (XEN)  L3[0x001] = 00000008668a3063 ffffffffffffffff
>     (XEN)  L2[0x000] = 000000086689c063 ffffffffffffffff
>     (XEN)  L1[0x004] = 000000056f078063 000000000007f678
>     (XEN)
>     (XEN) ****************************************
>     (XEN) Panic on CPU 7:
>     (XEN) FATAL PAGE FAULT
>     (XEN) [error_code=0000]
>     (XEN) Faulting linear address: ffff820040004ae0
>     (XEN) ****************************************
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> CC: Eddie Dong <eddie.dong@xxxxxxxxx>
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>

Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

 -George


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