Re: [Xen-devel] [PATCH] xen: only clobber multicall elements without error

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.11.18 at 14:25, <jgross@xxxxxxxx> wrote:
> In debug builds the hypervisor will deliberately clobber processed
> elements of the multicall structure. In order to ease diagnostic data
> printout in the affected guest only clobber elements which didn't
> return an error.

Besides what Andrew has said such a relaxation reduces
the guarding against bad guest side code. If a guest really
wishes to produce diagnostics, I think it should go to the
lengths of copying arguments (if they can't be re-calculated
anyway). Suppressing the clobbering in more cases merely
invites guests to read the arguments after the call, which
they simply should not do. Not clobbering the values in
release builds is a performance choice, and we ought to be
allowed to change our opinion regarding this implementation
detail at any point in time.

Jan



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