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Re: [PATCH] Revert "tools/firmware/ovmf: Use OvmfXen platform file is exist"

  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 22 Jun 2021 18:10:39 +0200
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  • Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 22 Jun 2021 16:10:49 +0000
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On 22.06.2021 17:39, Andrew Cooper wrote:
> This reverts commit aad7b5c11d51d57659978e04702ac970906894e8.
> The change from OvmfX64 to OvmfXen causes a change in behaviour, whereby
> OvmfXen maps its shared info page at the top of address space.  When trying to
> migrate such a domain, XENMEM_maximum_gpfn returns a very large value.  This
> has uncovered multiple issues:
>  1) The userspace hypercall wrappers truncate all return values to int on
>     Linux and Solaris.  This needs fixing in Xen.
>  2) 32bit toolstacks can't migrate any domain with RAM above the 2^40 mark,
>     because of virtual address constraints.  This needs fixing in OVMF.

And I suspect even that presently enforce boundary of 2^40 is actually
too high, and things still wouldn't work when getting close. At the
very least the tool stack then depends on a fairly big chunk of memory
(2^30 bytes) to be available in one single, virtually contiguous piece.
Iirc 32-bit Linux can be configured to not even leave this much space
for user mode.




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