Messages in this thread | | | Subject | Re: [PATCH 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace | From | "H. Peter Anvin" <> | Date | Tue, 30 Sep 2014 15:42:38 -0700 |
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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@linutronix.de> 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 >relevant. >> 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. > >Thanks, > > tglx
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