Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test

From: Borislav Petkov
Date: Mon Feb 29 2016 - 17:37:32 EST

On Mon, Feb 29, 2016 at 05:33:16PM -0500, Brian Gerst wrote:
> SYSENTER doesn't save EFLAGS so we have to fudge it by pushing the
> kernel's flags. Most user programs never set AC, so by adding it to
> the test for flags to clear we can avoid the CLAC or POPF in the
> common case that it is already clear.

Yeah, Andy just explained it to me on IRC. Thanks guys.


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