Re: [Xen-devel] [PATCH 0/2] MTRR/PAT virtualization

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 8/10/07 16:29, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:

> For RAM assigned to guest, the patch will allow non-WB types. The reason
> is for following scenerio: A  PCI-E device setting the non-snoop bit to
> 1 in TLP header when doing memory access transaction to RAM. and the
> driver/OS will access that RAM with UC attribute.
> 
> In current implementation without this patch, WB type will be used by
> guest, then PCI-E device may get wrong data, becaues the data updated
> by CPU may still in cache, and the PCI-E device's access is not snooped.
> This patch will virtualize the cache attribute through attribute in
> shadow page table.

Won't WBINVD and CLFLUSH also need to be virtualised?

If there are reservations about how this will interact with mappings in
qemu-dm, perhaps this new attribute mechanism should only be enabled for
pass-thru domains? We get no benefit for non-pass-thru domains and some
concern about correctness.

 -- Keir



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