Re: [PATCH] target/i386/mshv: Fix segment regression in MMIO emu

[Magnus Kulke <magnuskulke@linux.microsoft.com>]

On Sat, Apr 25, 2026 at 12:35:27AM +0300, Michael Tokarev wrote:
> On 10.04.2026 17:26, Magnus Kulke wrote:
> > When the segmentation code has been reworked, there is now an
> > unconditional call to emul_ops->read_segment_descriptor(). The MSHV impl
> > was delegating this to x86_read_segement_descriptor(), which read from
> > the GDT in guest memory. This fails for selector.idx == 0 and when no
> > GDT is set up (which is the case in real mode).
> > 
> > In the fix we change the MSHV impl to fill segment descriptor from
> > SegmentCache, that was populated from the hypervisor by mshv_load_regs()
> > before instruction emulation.
> > 
> > Fixes: 09442d98ab (target/i386: emulate: segmentation rework)
> > 
> > Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
> > ---
> >   target/i386/mshv/mshv-cpu.c | 39 ++++++++++++++++++++++++++++++-------
> >   1 file changed, 32 insertions(+), 7 deletions(-)
> 
> This looks like a qemu-stable material (11.0.x).
> 
> Please let me know if it isn't.
> 
> Thanks,
> 
> /mjt

I think so, yes. real mode mmio-emu will not work, which affects pretty
much all (x86) workloads for mshv.

best,

magnus