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Re: [PATCH v2 8/8] x86/PV: use get_unsafe() instead of copy_from_unsafe()
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Tue, 23 Feb 2021 12:59:22 +0100
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On Wed, Feb 17, 2021 at 09:23:33AM +0100, Jan Beulich wrote:
> The former expands to a single (memory accessing) insn, which the latter
> does not guarantee. Yet we'd prefer to read consistent PTEs rather than
> risking a split read racing with an update done elsewhere.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Albeit I wonder why the __builtin_constant_p check done in
copy_from_unsafe is not enough to take the get_unsafe_size branch in
there. Doesn't sizeof(l{1,2}_pgentry_t) qualify as a built time
constant?
Or the fact that n it's a parameter to an inline function hides this,
in which case the __builtin_constant_p is pointless?
Thanks, Roger.
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