Hi Mark, On Tue, 23 Dec 2025 at 01:22, Mark Brown <[email protected]> wrote: > > Provide versions of the SME state save and restore functions for the > hypervisor to allow it to restore ZA and ZT for guests. > > Signed-off-by: Mark Brown <[email protected]> > --- > arch/arm64/include/asm/kvm_hyp.h | 3 +++ > arch/arm64/kvm/hyp/fpsimd.S | 26 ++++++++++++++++++++++++++ > 2 files changed, 29 insertions(+) > > diff --git a/arch/arm64/include/asm/kvm_hyp.h > b/arch/arm64/include/asm/kvm_hyp.h > index 0317790dd3b7..1cef9991d238 100644 > --- a/arch/arm64/include/asm/kvm_hyp.h > +++ b/arch/arm64/include/asm/kvm_hyp.h > @@ -116,6 +116,9 @@ void __fpsimd_save_state(struct user_fpsimd_state > *fp_regs); > void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs); > void __sve_save_state(void *sve_pffr, u32 *fpsr, int save_ffr); > void __sve_restore_state(void *sve_pffr, u32 *fpsr, int restore_ffr); > +int __sve_get_vl(void); > +void __sme_save_state(void const *state, bool restore_zt); > +void __sme_restore_state(void const *state, bool restore_zt);
Would it be a good idea to pass the VL to these functions. Currently, they assume that the hardware's current VL matches the buffer's intended layout. But if there is a mismatch between the guest's VL and the current one, this could be difficult to debug. Passing the VL and checking it against _sme_rdsvl would be an inexpensive way to avoid these. > > u64 __guest_enter(struct kvm_vcpu *vcpu); > > diff --git a/arch/arm64/kvm/hyp/fpsimd.S b/arch/arm64/kvm/hyp/fpsimd.S > index 6e16cbfc5df2..44a1b0a483da 100644 > --- a/arch/arm64/kvm/hyp/fpsimd.S > +++ b/arch/arm64/kvm/hyp/fpsimd.S > @@ -29,3 +29,29 @@ SYM_FUNC_START(__sve_save_state) > sve_save 0, x1, x2, 3 > ret > SYM_FUNC_END(__sve_save_state) > + > +SYM_FUNC_START(__sve_get_vl) > + _sve_rdvl 0, 1 > + ret > +SYM_FUNC_END(__sve_get_vl) Since this is just one instruction, would it be better to implement it as an inline assembly in the header file rather than a full SYM_FUNC_START, to reduce the overhead? > + > +SYM_FUNC_START(__sme_save_state) I think that this needs an isb(). We need to ensure that SMCR updates are visible here. Looking ahead to where you introduce __hyp_sme_save_guest(), that doesn't have a barrier after updating SMCR. The alternative is to call the barrier where it's needed, but make sure that this is well documented. > + _sme_rdsvl 2, 1 // x2 = VL/8 > + sme_save_za 0, x2, 12 // Leaves x0 pointing to the end of ZA > + > + cbz x1, 1f > + _str_zt 0 > +1: > + ret > +SYM_FUNC_END(__sme_save_state) > + > +SYM_FUNC_START(__sme_restore_state) Same as above. Cheers, /fuad > + _sme_rdsvl 2, 1 // x2 = VL/8 > + sme_load_za 0, x2, 12 // Leaves x0 pointing to end of ZA > + > + cbz x1, 1f > + _ldr_zt 0 > + > +1: > + ret > +SYM_FUNC_END(__sme_restore_state) > > -- > 2.47.3 >
