[PATCH] arm64/sme: Fix EFI save/restore

[PATCH] arm64/sme: Fix EFI save/restore

[Mark Brown]

The EFI save/restore code is confused. When saving the check for saving
FFR is inverted due to confusion with the streaming mode check, and when
restoring we check if we need to restore FFR by checking the percpu
efi_sm_state without the required wrapper rather than based on the
combination of FA64 support and streaming mode.

Fixes: e0838f6373e5 ("arm64/sme: Save and restore streaming mode over EFI runtime calls")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---

Compile tested only at this point.

 arch/arm64/kernel/fpsimd.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 819979398127..3c66a061ff6f 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1916,10 +1916,11 @@ void __efi_fpsimd_begin(void)
 			if (system_supports_sme()) {
 				svcr = read_sysreg_s(SYS_SVCR);
 
-				if (!system_supports_fa64())
-					ffr = svcr & SVCR_SM_MASK;
+				__this_cpu_write(efi_sm_state,
+						 svcr & SVCR_SM_MASK);
 
-				__this_cpu_write(efi_sm_state, ffr);
+				if (!system_supports_fa64())
+					ffr = !(svcr & SVCR_SM_MASK);
 			}
 
 			sve_save_state(sve_state + sve_ffr_offset(sve_max_vl()),
@@ -1965,7 +1966,7 @@ void __efi_fpsimd_end(void)
 							   0,
 							   SVCR_SM_MASK);
 					if (!system_supports_fa64())
-						ffr = efi_sm_state;
+						ffr = false;
 				}
 			}
 
-- 
2.30.2


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Re: [PATCH] arm64/sme: Fix EFI save/restore

[Catalin Marinas]

On Thu, Jun 02, 2022 at 11:45:44AM +0200, Mark Brown wrote:
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index 819979398127..3c66a061ff6f 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -1916,10 +1916,11 @@ void __efi_fpsimd_begin(void)
>  			if (system_supports_sme()) {
>  				svcr = read_sysreg_s(SYS_SVCR);
>  
> -				if (!system_supports_fa64())
> -					ffr = svcr & SVCR_SM_MASK;
> +				__this_cpu_write(efi_sm_state,
> +						 svcr & SVCR_SM_MASK);
>  
> -				__this_cpu_write(efi_sm_state, ffr);
> +				if (!system_supports_fa64())
> +					ffr = !(svcr & SVCR_SM_MASK);
>  			}
>  
>  			sve_save_state(sve_state + sve_ffr_offset(sve_max_vl()),
> @@ -1965,7 +1966,7 @@ void __efi_fpsimd_end(void)
>  							   0,
>  							   SVCR_SM_MASK);
>  					if (!system_supports_fa64())
> -						ffr = efi_sm_state;
> +						ffr = false;
>  				}
>  			}

This looks fine to me:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Please add some comments to the code for when we need to save/restore
the FFR state and let me know when you got a chance to test it so that I
can send it upstream.

Thanks.

-- 
Catalin

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