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Re: [Xen-devel] [Bug] Intel RMRR support with upstream Qemu


On Mon, 24 Jul 2017 08:07:02 +0000
"Zhang, Xiong Y" <xiong.y.zhang@xxxxxxxxx> wrote:

> [Zhang, Xiong Y] Thanks for your suggestion.
> Indeed, if I set mmi_hole >= 4G - RMRR_Base, this could fix my issue.
> For this I still have two questions, could you help me ?
> 1) If hvmloader do low memory relocation, hvmloader and qemu will see a
> different guest memory layout . So qemu ram maybe overlop with mmio, does
> xen have plan to fix this ?
> 2) Just now, I did an experiment: In hvmloader, I set
> HVM_BELOW_4G_RAM_END to 3G and reserve one area for qemu_ram_allocate
> like 0xF0000000 ~ 0xFC000000; In Qemu, I modified xen_ram_alloc() to make
> sure it only allocate gfn in 0xF0000000 ~ 0xFC000000. In this case
> qemu_ram won't overlap with mmio, but this workaround couldn't fix my
> issue. It seems qemu still has another interface to allocate gfn except
> xen_ram_alloc(), do you know this interface ?

Please share your 'xl dmesg' output, to have a look at your guest's MMIO
map and which RMRRs and PCI MBARs are present there.

If RMRR range happens to overlap some guest's RAM below pci_start
(dictated by lack of relocation support and low_mem_pgend value), I think
your problem might be solved by sacrificing some part of guest RAM which is
overlapped by RMRR -- by changing the E820 map in hvmloader.

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