Re: [PATCH 2/2] x86/hvm: fix write emulation of RO ranges

[Marek Marczykowski <marmarek@invisiblethingslab.com>]

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On Tue, Apr 08, 2025 at 03:57:17PM +0200, Jan Beulich wrote:
> On 08.04.2025 11:31, Roger Pau Monne wrote:
> > When running on AMD hardware in HVM mode the guest linear address (GLA)
> > will not be provided to hvm_emulate_one_mmio(), and instead is
> > unconditionally set of ~0.  As a consequence mmio_ro_emulated_write() will
> > always report an error, as the fault GLA generated by the emulation of the
> > access won't be ~0.
> 
> Which means subpage_mmio_write_accept() is flawed, too, on AMD (or more
> generally whenever .gla_valid isn't set).

That may explain issues I see when using XHCI console on AMD (I can
crash the whole thing using sequence of driver binding/unbinding in
dom0). That's actually the hw12 runner in the other series, but tests
that are included in gitlab do not trigger the issue (fortunately?). But
also, it may be a different issue, as it affects PV dom0 too...

Anyway, I can probably test a patch if subpage_mmio_write_accept() works
as intended (I'll need to check if that path is exercised on AMD too as
it depends on xhci caps layout - it was definitely used on Intel).

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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