On Tue, 2023-10-24 at 09:32 -0700, Sean Christopherson wrote: > On Tue, Oct 24, 2023, Weijiang Yang wrote: > > On 10/21/2023 8:39 AM, Sean Christopherson wrote: > > > On Thu, Sep 14, 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. > > > > > > > > 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); > > > Shouldn't all the other calculations in this function also switch to fpu_kernel_cfg? > > > At the very least, this looks wrong when paired with the above: > > > > > > gfpu->uabi_size = sizeof(struct kvm_xsave); > > > if (WARN_ON_ONCE(fpu_user_cfg.default_size > gfpu->uabi_size)) > > > gfpu->uabi_size = fpu_user_cfg.default_size; > > > > Hi, Sean, > > Not sure what's your concerns. > > From my understanding fpu_kernel_cfg.default_size should include all enabled > > xfeatures in host (XCR0 | XSS), this is also expected for supporting all > > guest enabled xfeatures. gfpu->uabi_size only includes enabled user xfeatures > > which are operated via KVM uABIs(KVM_GET_XSAVE/KVM_SET_XSAVE/KVM_GET_XSAVE2), > > so the two sizes are relatively independent since guest supervisor xfeatures > > are saved/restored via GET/SET_MSRS interfaces. > > Ah, right, I keep forgetting that KVM's ABI can't use XRSTOR because it forces > the compacted format. > > This part still looks odd to me: > > gfpu->xfeatures = fpu_user_cfg.default_features; That should be indeed fpu_kernel_cfg.default_features. This variable is also currently hardly used, it only tracks which dynamic userspace features are enabled and KVM only uses it once (in fpu_enable_guest_xfd_features) > gfpu->perm = fpu_user_cfg.default_features; This variable I think is currently only set and never read. Note that current->group_leader->thread.fpu.guest_perm is actually initialized to fpu_kernel_cfg.default_features but the kernel components of it masked in the corresponding prctl (ARCH_GET_XCOMP_SUPP/ARCH_GET_XCOMP_GUEST_PERM/ARCH_REQ_XCOMP_GUEST_PERM). So I think that we also should use fpu_kernel_cfg.default_features here for the sake of not having uninitilized variable on 32 bit kernels, because the whole FPU permission thing I see is implemented for 64 bit kernels only. Or even better IMHO is to remove both variables and in fpu_enable_guest_xfd_features, just mask the xfeatures with the XFEATURE_MASK_USER_DYNAMIC instead. Best regards, Maxim Levitsky > > but I'm probably just not understanding something in the other patches changes yet. >
