[PATCH v2 4/8] KVM: arm64: Add save/restore support for FPMR

[Mark Brown]

On Thu, Aug 01, 2024 at 10:19:51AM +0100, Marc Zyngier wrote:

> index 6af179c6356d..2466dd231362 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -198,6 +198,15 @@ static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
>  	} else {
>  		__fpsimd_save_state(*host_data_ptr(fpsimd_state));
>  	}
> +
> +	if (kvm_has_fpmr(vcpu->kvm)) {

nVHE is faulting for me, apparently on the kvm_has_fpmr() check though I
ran out of time to actually figure out where exactly it is going wrong.
I'll have a further poke tomorrow.  Backtrace below.

> +		u64 fpmr = read_sysreg_s(SYS_FPMR);
> +
> +		if (unlikely(is_protected_kvm_enabled()))
> +			*host_data_ptr(fpmr) = fpmr;

That looks wrong until you remember what host_data_ptr() does but but
it's actually fine.  host_data_ptr() is looking inside the struct
kvm_host_data for the CPU rather than referencing the locally defined
variable fpmr here.  I do think it's worth avoiding the name collision
though, perhaps just avoid the temporary variable?

[ 1610.219274][  T247] kvm [247]: nVHE hyp panic at: [<ffffffc080ce3fc8>] __kvm_
nvhe_$x.262+0x24/0x38!
[ 1610.219435][  T247] kvm [247]: nVHE call trace:
[ 1610.219509][  T247] kvm [247]:  [<ffffffc080ce3c2c>] __kvm_nvhe_hyp_panic+0xb
4/0xf8
[ 1610.219657][  T247] kvm [247]:  [<ffffffc080ce3df4>] __kvm_nvhe_$x.238+0x14/0x60
[ 1610.219803][  T247] kvm [247]:  [<ffffffc080ce33f8>] __kvm_nvhe_$x.88+0x24/0x23c
[ 1610.219942][  T247] kvm [247]:  [<ffffffc080ce64b4>] __kvm_nvhe_$x.26+0x8/0x2c
[ 1610.220080][  T247] kvm [247]:  [<ffffffc080ce617c>] __kvm_nvhe_$x.1+0x9c/0xa4
[ 1610.220216][  T247] kvm [247]:  [<ffffffc080ce50fc>] __kvm_nvhe___skip_pauth_save+0x4/0x4
[ 1610.220356][  T247] kvm [247]: ---[ end nVHE call trace ]---
[ 1610.220435][  T247] kvm [247]: Hyp Offset: 0xffffff807fe00000
[ 1610.220566][  T247] Kernel panic - not syncing: HYP panic:
[ 1610.220566][  T247] PS:1624023c9 PC:0000004000ee3fc8 ESR:0000000096000004
[ 1610.220566][  T247] FAR:ffffff880115cd1c HPFAR:0000000000000000 PAR:1d00007edbadc8de
[ 1610.220566][  T247] VCPU:0000004801e88000
[ 1610.220743][  T247] CPU: 0 UID: 0 PID: 247 Comm: kvm-vcpu-0 Not tainted 6.11.0-rc1+ #247
[ 1610.220878][  T247] Hardware name: FVP Base RevC (DT)
[ 1610.220958][  T247] Call trace:
[ 1610.221023][  T247]  dump_backtrace+0xfc/0x140
[ 1610.221132][  T247]  show_stack+0x24/0x38
[ 1610.221239][  T247]  dump_stack_lvl+0x3c/0x118
[ 1610.221358][  T247]  dump_stack+0x18/0x40
[ 1610.221474][  T247]  panic+0x134/0x368
[ 1610.221609][  T247]  nvhe_hyp_panic_handler+0x114/0x1a0
[ 1610.221758][  T247]  kvm_arm_vcpu_enter_exit+0x54/0xc0
[ 1610.221895][  T247]  kvm_arch_vcpu_ioctl_run+0x494/0xa28
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