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Re: [PATCH] revert "hvmloader: PA range 0xfc000000-0xffffffff should be UC"


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Thu, 16 Dec 2021 10:54:08 +0100
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On Tue, Dec 14, 2021 at 09:21:22AM +0100, Jan Beulich wrote:
> This reverts commit c22bd567ce22f6ad9bd93318ad0d7fd1c2eadb0d.
> 
> While its description is correct from an abstract or real hardware pov,
> the range is special inside HVM guests. The range being UC in particular
> gets in the way of OVMF, which places itself at [FFE00000,FFFFFFFF].

I would assume this range to be unpopulated? Does hvmloader populate
it in order to place ovmf?

> While this is benign to epte_get_entry_emt() as long as the IOMMU isn't
> enabled for a guest, it becomes a very noticable problem otherwise: It
> takes about half a minute for OVMF to decompress itself into its
> designated address range.
> 
> And even beyond OVMF there's no reason to have e.g. the ACPI memory
> range marked UC.
> 
> Fixes: c22bd567ce22 ("hvmloader: PA range 0xfc000000-0xffffffff should be UC")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

This is just a hole from hvmloader PoV, so it's fine to not apply any
specific MTRR attributes.

Thanks, Roger.



 


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