Re: [RFC PATCH 2/8] x86/fpu/xstate: Fix guest fpstate allocation size calculation

[Sean Christopherson]

On Fri, Oct 20, 2023, Sean Christopherson wrote:
> On Wed, Sep 13, 2023, Yang Weijiang wrote:
> > Fix guest xsave area allocation size from fpu_user_cfg.default_size to
> > fpu_kernel_cfg.default_size so that the xsave area size is consistent
> > with fpstate->size set in __fpstate_reset().
> > 
> > With the fix, guest fpstate size is sufficient for KVM supported guest
> > xfeatures.
> > 
> > Fixes: 69f6ed1d14c6 ("x86/fpu: Provide infrastructure for KVM FPU cleanup");
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> > ---
> >  arch/x86/kernel/fpu/core.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> > index a86d37052a64..a42d8ad26ce6 100644
> > --- a/arch/x86/kernel/fpu/core.c
> > +++ b/arch/x86/kernel/fpu/core.c
> > @@ -220,7 +220,9 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
> >  	struct fpstate *fpstate;
> >  	unsigned int size;
> >  
> > -	size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
> > +	size = fpu_kernel_cfg.default_size +
> > +	       ALIGN(offsetof(struct fpstate, regs), 64);
> 
> This looks sketchy and incomplete.  I haven't looked at the gory details of
> fpu_user_cfg vs. fpu_kernel_cfg, but the rest of this function uses fpu_user_cfg,
> including a check on fpu_user_cfg.default_size.  That makes me think that changing
> just the allocation size isn't quite right.

Shoot, I didn't realize the CET virtualization series included this a day later.
I'll respond there.