[Xen-devel] Re: The memory type of non-RAM address is WB by default?

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

Why take any notice of guest MTRR/PAT in cases where the host knows better?

 -- Keir

On 23/10/08 10:36, "Cui, Dexuan" <dexuan.cui@xxxxxxxxx> wrote:

> In changeset 17471:cd5dc735bdf3(x86, hvm: Lots of MTRR/PAT emulation cleanup),
> the default memory type is set to WB and the type of each special memory range
> is set properly. Specially, [3.75G, 4G) is assumed as PCI space and marked as
> UC.
> 
> I meet with an issue:
> When I "xm pci-attach" a NIC into RHEL5.1 Linux guest(memory=256M), the
> virtual MMIO BAR assigned by guest starts from 0x20000000 and I don't find
> guest kernel tries to set the MTRR registers at all; as a result, the type of
> the pfn is WB, but in hypervisor, the host mfn is UC, so when guest accesses
> the vBAR, there are many lines of such warnings printed:
> 
> (XEN) mtrr.c:400:d10 Conflict occurs for a given guest l1e flags:163 at
> 20000000 (the effective mm type:6), because the host mtrr type is:0
> 
> Here I think the device should work normally since the actual host mfn  is UC,
> but we might as well fix such inconsistency.
> Can't we set the default type to UC?
> 
> BTW: when I statically assign a NIC to guest via config file, since the vBAR
> assigned by hvmloader starts from 0xF0000000, I don't see the warnings.
> 
> Thanks,
> -- Dexuan
> 
> 
> 



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