[PATCH v2] arm64: Do not trap PMSNEVFR_EL1

[Marc Zyngier]

On Tue, 24 Aug 2021 16:45:23 +0100,
Alexandru Elisei <alexandru.elisei at arm.com> wrote:
> 
> Commit 31c00d2aeaa2 ("arm64: Disable fine grained traps on boot") zeroed
> the fine grained trap registers to prevent unwanted register traps from
> occuring. However, for the PMSNEVFR_EL1 register, the corresponding
> HDFG{R,W}TR_EL2.nPMSNEVFR_EL1 fields must be 1 to disable trapping. Set
> both fields to 1 if FEAT_SPEv1p2 is detected to disable read and write
> traps.
> 
> Fixes: 31c00d2aeaa2 ("arm64: Disable fine grained traps on boot")
> Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
> ---
> Based on v5.14-rc7. Tested on the model, using boot-wrapper built from
> commit 5cd6238ec4ef ("aarch32: fix .globl replacement"). Without this
> patch, in NVHE mode, the model freezes when I try to access PMSNEVFR_EL1.
> With this patch, the model doesn't hang anymore.
> 
> Changes since v1:
> 
> * Set the corresponding bit in HDFGWRTR_EL2 to also disable write traps. My
>   thanks to Mark for pointing it out.
> 
>  arch/arm64/include/asm/el2_setup.h | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
> index b83fb24954b7..3198acb2aad8 100644
> --- a/arch/arm64/include/asm/el2_setup.h
> +++ b/arch/arm64/include/asm/el2_setup.h
> @@ -149,8 +149,17 @@
>  	ubfx	x1, x1, #ID_AA64MMFR0_FGT_SHIFT, #4
>  	cbz	x1, .Lskip_fgt_\@
>  
> -	msr_s	SYS_HDFGRTR_EL2, xzr
> -	msr_s	SYS_HDFGWTR_EL2, xzr
> +	mov	x0, xzr
> +	mrs	x1, id_aa64dfr0_el1
> +	ubfx	x1, x1, #ID_AA64DFR0_PMSVER_SHIFT, #4
> +	cmp	x1, #3
> +	b.lt	.Lset_fgt_\@
> +	/* Disable PMSNEVFR_EL1 read and write traps */
> +	orr	x0, x0, #(1 << 62)
> +
> +.Lset_fgt_\@:
> +	msr_s	SYS_HDFGRTR_EL2, x0
> +	msr_s	SYS_HDFGWTR_EL2, x0
>  	msr_s	SYS_HFGRTR_EL2, xzr
>  	msr_s	SYS_HFGWTR_EL2, xzr
>  	msr_s	SYS_HFGITR_EL2, xzr

The beauty of negative trap bits... Thankfully this seems to be the
only one.

Acked-by: Marc Zyngier <maz at kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.