On Fri, Mar 01, 2019 at 01:49:10AM +1100, Michael Ellerman wrote:
> In order to implement KUAP (Kernel Userspace Access Protection) on
> Power9 we will be using the AMR, and therefore indirectly the
> UAMOR/AMOR.
>
> So save/restore these regs in the idle code.
>
> Signed-off-by: Michael Ellerman
> ---
> arch/powerpc/kernel/idle_book3s.S | 27 +++
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> v4: New.
>
> diff --git a/arch/powerpc/kernel/idle_book3s.S
> b/arch/powerpc/kernel/idle_book3s.S
> index 36178000a2f2..4a860d3b9229 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -170,8 +170,11 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
> bne-core_idle_lock_held
> blr
>
> -/* Reuse an unused pt_regs slot for IAMR */
> +/* Reuse some unused pt_regs slots for AMR/IAMR/UAMOR/UAMOR */
> +#define PNV_POWERSAVE_AMR_TRAP
> #define PNV_POWERSAVE_IAMR _DAR
> +#define PNV_POWERSAVE_UAMOR _DSISR
> +#define PNV_POWERSAVE_AMOR RESULT
>
> /*
> * Pass requested state in r3:
> @@ -205,8 +208,16 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
> SAVE_NVGPRS(r1)
>
> BEGIN_FTR_SECTION
> + mfspr r4, SPRN_AMR
> mfspr r5, SPRN_IAMR
> + mfspr r6, SPRN_UAMOR
> + std r4, PNV_POWERSAVE_AMR(r1)
> std r5, PNV_POWERSAVE_IAMR(r1)
> + std r6, PNV_POWERSAVE_UAMOR(r1)
> +BEGIN_FTR_SECTION_NESTED(42)
> + mfspr r7, SPRN_AMOR
> + std r7, PNV_POWERSAVE_AMOR(r1)
> +END_FTR_SECTION_NESTED_IFSET(CPU_FTR_HVMODE, 42)
> END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
Can we save/restore for ARCH_300S only ?
I checked the user manual "POWER8 Processor User’s Manual for the
Single-Chip Module" v1.3 dated 16 March 2016. In section 9.7.2.2,
It mentions that AMOR and UAMOR will be preserved by hardware.
Excrept :
" When an SMT thread switch is enabled, the napping thread’s
resources can be given to other threads to improve core
performance. Software must restore the architected state
of the dormant thread upon exiting nap mode except for
the following architected facilities, which are preserved
by the hardware:
- SLB State
- All Hypervisor Special Registers (includes PURR, SPURR, AMOR,
UAMOR, AMR, ACOP)
"
Keeping 207S has no harm, its just that we may spend a few
more cycles saving and restoring the sprs.
>
> mfcrr5
> @@ -935,12 +946,20 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
> REST_GPR(2, r1)
>
> BEGIN_FTR_SECTION
> - /* IAMR was saved in pnv_powersave_common() */
> + /* These regs were saved in pnv_powersave_common() */
> + ld r4, PNV_POWERSAVE_AMR(r1)
> ld r5, PNV_POWERSAVE_IAMR(r1)
> + ld r6, PNV_POWERSAVE_UAMOR(r1)
> + mtspr SPRN_AMR, r4
> mtspr SPRN_IAMR, r5
> + mtspr SPRN_UAMOR, r6
> +BEGIN_FTR_SECTION_NESTED(42)
> + ld r7, PNV_POWERSAVE_AMOR(r1)
> + mtspr SPRN_AMOR, r7
> +END_FTR_SECTION_NESTED_IFSET(CPU_FTR_HVMODE, 42)
> /*
> - * We don't need an isync here because the upcoming mtmsrd is
> - * execution synchronizing.
> + * We don't need an isync here after restoring IAMR because the upcoming
> + * mtmsrd is execution synchronizing.
>*/
> END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>
> --
> 2.20.1
>
