Subject: Re: powerpc/process: fix altivec SPR not being saved

From: Michael Ellerman <[email-masked]>
Date: Thu, 31 Mar 2016 10:29:45 +1100 (AEDT)

On Mon, 2016-07-03 at 22:08:47 UTC, Oliver O'Halloran wrote:
> In save_sprs() in process.c contains the following test:
> 
> 	if (cpu_has_feature(cpu_has_feature(CPU_FTR_ALTIVEC)))
> 		t->vrsave = mfspr(SPRN_VRSAVE);
> 
> CPU feature with the mask 0x1 is CPU_FTR_COHERENT_ICACHE so the test
> is equivilent to:
> 
> 	if (cpu_has_feature(CPU_FTR_ALTIVEC) &&
> 		cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
> 
> On CPUs without support for both (i.e G5) this results in vrsave not being
> saved between context switches. The vector register save/restore code
> doesn't use VRSAVE to determine which registers to save/restore,
> but the value of VRSAVE is used to determine if altivec is being used
> in several code paths.
> 
> Signed-off-by: Oliver O'Halloran <[email-masked]>
> Signed-off-by: Anton Blanchard <[email-masked]>
> Fixes: 152d523e6307 ("powerpc: Create context switch helpers save_sprs() and restore_sprs()")
> Cc: [email-masked]

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/01d7c2a2de47890934faba91a7

cheers