On Thu, Feb 06, 2025 at 02:10:55PM +0000, Mark Rutland wrote: > There are several problems with the way hyp code lazily saves the host's > FPSIMD/SVE state, including: > > * Host SVE being discarded unexpectedly due to inconsistent > configuration of TIF_SVE and CPACR_ELx.ZEN. This has been seen to > result in QEMU crashes where SVE is used by memmove(), as reported by > Eric Auger: > > https://issues.redhat.com/browse/RHEL-68997 > > * Host SVE state is discarded *after* modification by ptrace, which was an > unintentional ptrace ABI change introduced with lazy discarding of SVE state. > > * The host FPMR value can be discarded when running a non-protected VM, > where FPMR support is not exposed to a VM, and that VM uses > FPSIMD/SVE. In these cases the hyp code does not save the host's FPMR > before unbinding the host's FPSIMD/SVE/SME state, leaving a stale > value in memory. How hard would it be to write tests for these three scenarios? If we had something to exercise the relevant paths then... > ... and so this eager save+flush probably needs to be backported to ALL > stable trees. ... this backporting might be a little easier to be sure about? Will
