Re: [Xen-devel] [PATCH v2 11/16] x86/PV: split out dealing with DRn from privileged instruction handling

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/09/16 09:15, Jan Beulich wrote:
> This is in preparation for using the generic emulator here.
>
> Some care is needed temporarily to not unduly alter guest register
> state: The local variable "res" can only go away once this code got
> fully switched over to using x86_emulate().
>
> Also switch to IS_ERR_VALUE() instead of (incorrectly) open coding it.

It isn't actually an ERR_PTR().  That bit of code pre-dates the
introduction of ERR_PTR() by some margin.

The return code of do_get_debugreg() is broken and needs fixing, along
with the ABI of the debugreg hypercalls.

This change does cause an ABI change for PV guests, as they now can't
read a debug register whose value is in the top 4k of linear address
space, (ather than the top 8th of a page previously), but given that the
ABI is already known broken, I am not sure I care too much.

Either way, keeping it like this, or switching back to the previous
opencoding, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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