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Re: [Xen-devel] [PATCH] x86: refine debugging of SMEP/SMAP fix

>>> On 17.05.16 at 12:28, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 17/05/16 10:54, Jan Beulich wrote:
>> Instead of just latching cr4_pv32_mask into %rdx, correct the found
>> wrong value in %cr4 (to avoid triggering another BUG). The value left
>> in %rdx should be sufficient for deducing cr4_pv32_mask from the
>> register dump.
> Alternatively, you can reuse %rax (as its value is useless by this
> point) and leave %rdx as exactly cr4_pv32_mask.  This avoids needing a
> subsequent step to reverse engineer cr4_pv32_mask.

I don't view the value in %rax as useless - that's the set of bits
we have found set, which didn't match our expectation. Hence I
specifically don't want to re-use that register.


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