On Wed, Jun 13, 2018 at 07:01:23PM +0200, Paolo Bonzini wrote: > On 12/06/2018 20:25, Eduardo Habkost wrote: > > On Tue, Jun 12, 2018 at 05:12:58PM +0200, Paolo Bonzini wrote: > >> On 12/06/2018 17:01, Eduardo Habkost wrote: > >>>>> > >>>>> Remove OSPKE from the feature name array so users don't try to > >>>>> configure it manually. > >>>>> > >>>>> Signed-off-by: Eduardo Habkost <ehabk...@redhat.com> > >>>> Yes, it's the same as OSXSAVE. Thanks! > >>> CR4_OSXSAVE_MASK is automatically enabled on user-mode QEMU, > >>> though. > >>> > >>> My question is if it would make any sense to enable CR4_PKE_MASK > >>> too. > >> > >> If you mean OSPKE, then yes---if PKU is available. Likewise, OSXSAVE > >> should only be enabled if XSAVE is available. > > > > Yeah, I mean enabling it only if PKU is available, like we > > already do with OSXAVE/XSAVE. > > > > But we don't do it today, so enabling it automatically in > > CONFIG_USER_ONLY would be a new feature. Would it be useful for > > anything, though? > > > > I'm asking that to find out if somebody could be already using > > "-cpu ...,+ospke" with user-mode QEMU today (which this patch > > would break). If RDPKRU/WRPKRU is useless under user-mode QEMU, > > than we don't need to worry about that. > > Hmm, actually there are two more things to consider for user-mode emulation. > > First, QEMU doesn't support any of pkey_mprotect, pkey_alloc, pkey_free, > so it should probably never set OSPKE.
This means "-cpu ...,+ospke" is useless today and we can safely remove support for it, right? > Second, for user-mode emulation it makes sense to allow flipping of > OSPKE and OSXSAVE, because that corresponds to different behaviors of > the underlying kernels. There have been bugs in fact with programs that > incorrectly tested XSAVE instead of OSXSAVE, so it's worthwhile to let > the user test both configurations. However, "-cpu ...,-osxsave" has no effect today (user-mode QEMU unconditionally sets OSXSAVE), so that would be a new feature. I assume this means I don't need to drop the osxsave patch from my queue, either. > So to sum up, the default for QEMU user-mode emulation should be > OSXSAVE=XSAVE and OSPKE=0. Thanks! -- Eduardo
