Re: [Xen-devel] [PATCH for-4.11] x86/traps: Fix error handling of the pv %dr7 shadow state

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.06.18 at 16:06, <andrew.cooper3@xxxxxxxxxx> wrote:
> c/s "x86/pv: Introduce and use x86emul_write_dr()" fixed a bug with IO shadow
> handling, in that it remained stale and visible until %dr7.L/G got set again.
> 
> However, it neglected the -EPERM return inbetween these two hunks, introducing
> a different bug in which a write to %dr7 which tries to set IO breakpoints
> without %cr4.DE being set clobbers the IO state, rather than leaves it alone.
> 
> Instead, move the zeroing slightly later, which guarentees that the shadow
> gets written exactly once, on a successful update to %dr7.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>



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