Re: [PATCH 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace

From: H. Peter Anvin
Date: Tue Sep 30 2014 - 18:43:38 EST

Nicely enough we get the context switch benefit without any cost in the comon case of 64-bit apps.

On September 30, 2014 3:27:41 PM PDT, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>On Tue, 30 Sep 2014, Andy Lutomirski wrote:
>> It would certainly be possible to clear NT and retry IRET if IRET
>> fails with NT set. This would have no overhead for anything
>> That would be this alternative from my 0/2 email:
>> - Don't filter NT on sysenter. Instead, filter it on EFI entry
>> and modify the IRET code to retry without NT set if NT was set.
>> Thomas hpa, etc: any thoughts?
>Filter it right away. That's solid and obvious. Anything else is just
>complex and prone for future brown paperbag failures.
>We get the context switch benefit from it, so there is some
>compensation for the extra cycles.
> tglx

Sent from my mobile phone. Please pardon brevity and lack of formatting.
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