> On Mar 29, 2021, at 9:06 AM, Len Brown <l...@kernel.org> wrote: > > On Mon, Mar 29, 2021 at 11:43 AM Len Brown <l...@kernel.org> wrote: >> >> On Mon, Mar 29, 2021 at 9:33 AM Thomas Gleixner <t...@linutronix.de> wrote: >> >>>> I found the author of this passage, and he agreed to revise it to say this >>>> was targeted primarily at VMMs. >>> >>> Why would this only a problem for VMMs? >> >> VMMs may have to emulate different hardware for different guest OS's, >> and they would likely "context switch" XCR0 to achieve that. >> >> As switching XCR0 at run-time would confuse the heck out of user-space, >> it was not imagined that a bare-metal OS would do that. > > to clarify... > *switching* XCR0 on context switch is slow, but perfectly legal.
How slow is it? And how slow is switching XFD? XFD is definitely serializing?
