On Fri, Dec 28, 2018 at 12:39:35PM +0000, Andrew Cooper wrote: > AMD hardware before Zen doesn't safe/restore the FPU error pointers > unless an unmasked FPU exception is pending. Zen processors have a > feature bit indicating that this (mis)behaviour no longer exists. > > Express the common logic in terms of cpu_bug_fpu_err_ptr as Hygon > processors (being Zen derivatives) won't inherit this behaviour. > > While at it, fix a performance issue with the workaround, which I should > have noticed by now. Looking at the FPU state slows the context switch > path down, as it is a moderately complicated unpredictable condition > which will evaluate to true for all 64bit OSes and most 32bit ones. > > Leave the sole condition being the easily-predictable > cpu_bug_fpu_err_ptr as the asm sequence is needed in ~100% of cases > these days on affected hardware.
I'm not that familiar with the FPU registers, but I assume current code checks whether there's an exception pending before decoding whether the error pointers should be cleared? > Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> Apart from the question above, LGTM: Reviewed-by: Roger Pau Monné <roger....@citrix.com> Thanks. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
