| Message ID | 20250404174435.3288106-9-mark.rutland@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | arm64: Preparatory FPSIMD/SVE/SME fixes | expand |
On Fri, Apr 04, 2025 at 06:44:29PM +0100, Mark Rutland wrote: > On system with SME, a thread's kernel FPSIMD state may be erroneously > clobbered during a context switch immediately after that state is > restored. Systems without SME are unaffected. Reviewed-by: Mark Brown <broonie@kernel.org>
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index b19736f354a71..4a0b0bb3a3fad 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -1550,8 +1550,8 @@ void fpsimd_thread_switch(struct task_struct *next) fpsimd_save_user_state(); if (test_tsk_thread_flag(next, TIF_KERNEL_FPSTATE)) { - fpsimd_load_kernel_state(next); fpsimd_flush_cpu_state(); + fpsimd_load_kernel_state(next); } else { /* * Fix up TIF_FOREIGN_FPSTATE to correctly describe next's
On system with SME, a thread's kernel FPSIMD state may be erroneously clobbered during a context switch immediately after that state is restored. Systems without SME are unaffected. If the CPU happens to be in streaming SVE mode before a context switch to a thread with kernel FPSIMD state, fpsimd_thread_switch() will restore the kernel FPSIMD state using fpsimd_load_kernel_state() while the CPU is still in streaming SVE mode. When fpsimd_thread_switch() subsequently calls fpsimd_flush_cpu_state(), this will execute an SMSTOP, causing an exit from streaming SVE mode. The exit from streaming SVE mode will cause the hardware to reset a number of FPSIMD/SVE/SME registers, clobbering the FPSIMD state. Fix this by calling fpsimd_flush_cpu_state() before restoring the kernel FPSIMD state. Fixes: e92bee9f861b466c ("arm64/fpsimd: Avoid erroneous elide of user state reload") Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Mark Brown <broonie@kernel.org> Cc: Will Deacon <will@kernel.org> --- arch/arm64/kernel/fpsimd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)