On Fri Sep 16, 2022 at 3:32 PM AEST, Rohan McLure wrote:
> Restoring the register state of the interrupted thread involves issuing
> a large number of predictable loads to the kernel stack frame. Issue the
> REST_GPR{,S} macros to clearly signal when this is happening, and bunch
> together restores at the end of the interrupt handler where the saved
> value is not consumed earlier in the handler code.
>
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
> Reported-by: Christophe Leroy <christophe.leroy at csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> V2 -> V3: New patch.
> V3 -> V4: Minimise restores in the unrecoverable window between
> restoring SRR0/1 and return from interrupt.
> ---
> arch/powerpc/kernel/entry_32.S | 33 +++++++++++++-------------------
> 1 file changed, 13 insertions(+), 20 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 44dfce9a60c5..e4b694cebc44 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -68,7 +68,7 @@ prepare_transfer_to_handler:
> lwz r9,_MSR(r11) /* if sleeping, clear MSR.EE */
> rlwinm r9,r9,0,~MSR_EE
> lwz r12,_LINK(r11) /* and return to address in LR */
> - lwz r2, GPR2(r11)
> + REST_GPR(2, r11)
> b fast_exception_return
> _ASM_NOKPROBE_SYMBOL(prepare_transfer_to_handler)
> #endif /* CONFIG_PPC_BOOK3S_32 || CONFIG_E500 */
> @@ -144,7 +144,7 @@ ret_from_syscall:
> lwz r7,_NIP(r1)
> lwz r8,_MSR(r1)
> cmpwi r3,0
> - lwz r3,GPR3(r1)
> + REST_GPR(3, r1)
> syscall_exit_finish:
> mtspr SPRN_SRR0,r7
> mtspr SPRN_SRR1,r8
> @@ -152,8 +152,8 @@ syscall_exit_finish:
> bne 3f
> mtcr r5
>
> -1: lwz r2,GPR2(r1)
> - lwz r1,GPR1(r1)
> +1: REST_GPR(2, r1)
> + REST_GPR(1, r1)
> rfi
> #ifdef CONFIG_40x
> b . /* Prevent prefetch past rfi */
> @@ -165,10 +165,8 @@ syscall_exit_finish:
> REST_NVGPRS(r1)
> mtctr r4
> mtxer r5
> - lwz r0,GPR0(r1)
> - lwz r3,GPR3(r1)
> - REST_GPRS(4, 11, r1)
> - lwz r12,GPR12(r1)
> + REST_GPR(0, r1)
> + REST_GPRS(3, 12, r1)
> b 1b
>
> #ifdef CONFIG_44x
> @@ -260,9 +258,8 @@ fast_exception_return:
> beq 3f /* if not, we've got problems */
> #endif
>
> -2: REST_GPRS(3, 6, r11)
> - lwz r10,_CCR(r11)
> - REST_GPRS(1, 2, r11)
> +2: lwz r10,_CCR(r11)
> + REST_GPRS(1, 6, r11)
> mtcr r10
> lwz r10,_LINK(r11)
> mtlr r10
> @@ -277,7 +274,7 @@ fast_exception_return:
> mtspr SPRN_SRR0,r12
> REST_GPR(9, r11)
> REST_GPR(12, r11)
> - lwz r11,GPR11(r11)
> + REST_GPR(11, r11)
> rfi
> #ifdef CONFIG_40x
> b . /* Prevent prefetch past rfi */
> @@ -454,9 +451,8 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return)
> lwz r3,_MSR(r1); \
> andi. r3,r3,MSR_PR; \
> bne interrupt_return; \
> - lwz r0,GPR0(r1); \
> - lwz r2,GPR2(r1); \
> - REST_GPRS(3, 8, r1); \
> + REST_GPR(0, r1); \
> + REST_GPRS(2, 8, r1); \
> lwz r10,_XER(r1); \
> lwz r11,_CTR(r1); \
> mtspr SPRN_XER,r10; \
> @@ -475,11 +471,8 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return)
> lwz r12,_MSR(r1); \
> mtspr exc_lvl_srr0,r11; \
> mtspr exc_lvl_srr1,r12; \
> - lwz r9,GPR9(r1); \
> - lwz r12,GPR12(r1); \
> - lwz r10,GPR10(r1); \
> - lwz r11,GPR11(r1); \
> - lwz r1,GPR1(r1); \
> + REST_GPRS(9, 12, r1); \
> + REST_GPR(1, r1); \
> exc_lvl_rfi; \
> b .; /* prevent prefetch past exc_lvl_rfi */
>
> --
> 2.34.1