* Dave Hansen:
On 5/21/21 7:44 AM, Florian Weimer wrote:
quoted
* Dave Hansen via Libc-alpha:
quoted
Our system calls are *REALLY* fast. We can even do a vsyscall for this
if we want to get the overhead down near zero. Userspace can also cache
the "I did the prctl()" state in thread-local storage if it wants to
avoid the syscall.
Why can't userspace look at XCR0 to make the decision?
The thing we're trying to avoid is a #NM exception from XFD (the new
first-use detection feature) that occurs on the first use of AMX.
XCR0 will have XCR0[AMX]=1, even if XFD is "armed" and ready to
generate the #NM.
I see. So essentially the hardware wants to offer transparent
initialize-on-use, but Linux does not seem to want to implement it this
way.
Is there still a chance to bring the hardware and Linux into alignment?
Thanks,
Florian