Andy Chiu <andy.chiu@xxxxxxxxxx> writes: > Hey Björn, > > On Tue, Feb 14, 2023 at 2:43 PM Björn Töpel <bjorn@xxxxxxxxxx> wrote: >> So, two changes: >> >> 1. Disallow V-enablement if the existing altstack does not fit a V-sized >> frame. > This could potentially break old programs (non-V) that load new system > libraries (with V), If the program sets a small alt stack and takes > the fault in some libraries that use V. However, existing > implementation will also kill the process when the signal arrives, > finding insufficient stack frame in such cases. I'd choose the second > one if we only have these two options, because there is a chance that > the signal handler may not even run. I think we might have different views here. A process has a pre-V, a and post-V state. Is allowing a process to enter V without the correct preconditions a good idea? Allow to run with V turned on, but not able to correctly handle a signal (the stack is too small)? This was the same argument that the Intel folks had when enabling AMX. Sure, AMX requires *explicit* enablement, but same rules should apply, no? >> 2. Sanitize altstack changes when V is enabled. > Yes, I'd like to have this. But it may be tricky when it comes to > deciding whether V is enabled, due to the first-use trap. If V is > commonly used in system libraries then it is likely that V will be > enabled before an user set an altstack. Sanitizing this case would be > easy and straightforward. But what if the user sets an altstack before > enabling V in the first-use trap? This could happen on a statically > program that has hand-written V routines. This takes us to the 1st > question above, should we fail the user program immediately if the > altstack is set too small? For me it's obvious to fail (always) "if the altstack is too small to enable V", because it allows to execute V without proper preconditions. Personally, I prefer a stricter model. Only enter V if you can, and after entering it disallow changing the altstack. Then again, this is *my* opinion and concern. What do other people think? I don't want to stall the series. >> >> Other than the altstack handling, I think the series is a good state! It >> would great if we could see a v14 land in -next... > Thanks. I am reforming the v14 patch and hoping the same to happen soon too! Thank you for your hard work! It would be awesome to *finally* have vector support in the kernel! Björn
