powerpc/64s: system call support for scv/rfscv instructions

Add support for the scv instruction on POWER9 and later CPUs.

For now this implements the zeroth scv vector 'scv 0', as identical to
'sc' system calls, with the exception that LR is not preserved, nor
are volatile CR registers, and error is not indicated with CR0[SO],
but by returning a negative errno.

rfscv is implemented to return from scv type system calls. It can not
be used to return from sc system calls because those are defined to
preserve LR.

getpid syscall throughput on POWER9 is improved by 26% (428 to 318
cycles), largely due to reducing mtmsr and mtspr.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Fix ppc64e build]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200611081203.995112-3-npiggin@gmail.com

1 files changed, 169 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 9d49338e0c85..223c4f008e63 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -64,15 +64,173 @@ exception_marker:
 	.section	".text"
 	.align 7
 
+#ifdef CONFIG_PPC_BOOK3S
+.macro system_call_vectored name trapnr
+	.globl system_call_vectored_\name
+system_call_vectored_\name:
+_ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+BEGIN_FTR_SECTION
+	extrdi.	r10, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */
+	bne	.Ltabort_syscall
+END_FTR_SECTION_IFSET(CPU_FTR_TM)
+#endif
+	INTERRUPT_TO_KERNEL
+	mr	r10,r1
+	ld	r1,PACAKSAVE(r13)
+	std	r10,0(r1)
+	std	r11,_NIP(r1)
+	std	r12,_MSR(r1)
+	std	r0,GPR0(r1)
+	std	r10,GPR1(r1)
+	std	r2,GPR2(r1)
+	ld	r2,PACATOC(r13)
+	mfcr	r12
+	li	r11,0
+	/* Can we avoid saving r3-r8 in common case? */
+	std	r3,GPR3(r1)
+	std	r4,GPR4(r1)
+	std	r5,GPR5(r1)
+	std	r6,GPR6(r1)
+	std	r7,GPR7(r1)
+	std	r8,GPR8(r1)
+	/* Zero r9-r12, this should only be required when restoring all GPRs */
+	std	r11,GPR9(r1)
+	std	r11,GPR10(r1)
+	std	r11,GPR11(r1)
+	std	r11,GPR12(r1)
+	std	r9,GPR13(r1)
+	SAVE_NVGPRS(r1)
+	std	r11,_XER(r1)
+	std	r11,_LINK(r1)
+	std	r11,_CTR(r1)
+
+	li	r11,\trapnr
+	std	r11,_TRAP(r1)
+	std	r12,_CCR(r1)
+	std	r3,ORIG_GPR3(r1)
+	addi	r10,r1,STACK_FRAME_OVERHEAD
+	ld	r11,exception_marker@toc(r2)
+	std	r11,-16(r10)		/* "regshere" marker */
+
+	/*
+	 * RECONCILE_IRQ_STATE without calling trace_hardirqs_off(), which
+	 * would clobber syscall parameters. Also we always enter with IRQs
+	 * enabled and nothing pending. system_call_exception() will call
+	 * trace_hardirqs_off().
+	 *
+	 * scv enters with MSR[EE]=1, so don't set PACA_IRQ_HARD_DIS. The
+	 * entry vector already sets PACAIRQSOFTMASK to IRQS_ALL_DISABLED.
+	 */
+
+	/* Calling convention has r9 = orig r0, r10 = regs */
+	mr	r9,r0
+	bl	system_call_exception
+
+.Lsyscall_vectored_\name\()_exit:
+	addi    r4,r1,STACK_FRAME_OVERHEAD
+	li	r5,1 /* scv */
+	bl	syscall_exit_prepare
+
+	ld	r2,_CCR(r1)
+	ld	r4,_NIP(r1)
+	ld	r5,_MSR(r1)
+
+BEGIN_FTR_SECTION
+	stdcx.	r0,0,r1			/* to clear the reservation */
+END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
+
+BEGIN_FTR_SECTION
+	HMT_MEDIUM_LOW
+END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
+
+	cmpdi	r3,0
+	bne	.Lsyscall_vectored_\name\()_restore_regs
+
+	/* rfscv returns with LR->NIA and CTR->MSR */
+	mtlr	r4
+	mtctr	r5
+
+	/* Could zero these as per ABI, but we may consider a stricter ABI
+	 * which preserves these if libc implementations can benefit, so
+	 * restore them for now until further measurement is done. */
+	ld	r0,GPR0(r1)
+	ld	r4,GPR4(r1)
+	ld	r5,GPR5(r1)
+	ld	r6,GPR6(r1)
+	ld	r7,GPR7(r1)
+	ld	r8,GPR8(r1)
+	/* Zero volatile regs that may contain sensitive kernel data */
+	li	r9,0
+	li	r10,0
+	li	r11,0
+	li	r12,0
+	mtspr	SPRN_XER,r0
+
+	/*
+	 * We don't need to restore AMR on the way back to userspace for KUAP.
+	 * The value of AMR only matters while we're in the kernel.
+	 */
+	mtcr	r2
+	ld	r2,GPR2(r1)
+	ld	r3,GPR3(r1)
+	ld	r13,GPR13(r1)
+	ld	r1,GPR1(r1)
+	RFSCV_TO_USER
+	b	.	/* prevent speculative execution */
+
+.Lsyscall_vectored_\name\()_restore_regs:
+	li	r3,0
+	mtmsrd	r3,1
+	mtspr	SPRN_SRR0,r4
+	mtspr	SPRN_SRR1,r5
+
+	ld	r3,_CTR(r1)
+	ld	r4,_LINK(r1)
+	ld	r5,_XER(r1)
+
+	REST_NVGPRS(r1)
+	ld	r0,GPR0(r1)
+	mtcr	r2
+	mtctr	r3
+	mtlr	r4
+	mtspr	SPRN_XER,r5
+	REST_10GPRS(2, r1)
+	REST_2GPRS(12, r1)
+	ld	r1,GPR1(r1)
+	RFI_TO_USER
+.endm
+
+system_call_vectored common 0x3000
+/*
+ * We instantiate another entry copy for the SIGILL variant, with TRAP=0x7ff0
+ * which is tested by system_call_exception when r0 is -1 (as set by vector
+ * entry code).
+ */
+system_call_vectored sigill 0x7ff0
+
+
+/*
+ * Entered via kernel return set up by kernel/sstep.c, must match entry regs
+ */
+	.globl system_call_vectored_emulate
+system_call_vectored_emulate:
+_ASM_NOKPROBE_SYMBOL(system_call_vectored_emulate)
+	li	r10,IRQS_ALL_DISABLED
+	stb	r10,PACAIRQSOFTMASK(r13)
+	b	system_call_vectored_common
+#endif
+
+	.balign IFETCH_ALIGN_BYTES
 	.globl system_call_common
 system_call_common:
+_ASM_NOKPROBE_SYMBOL(system_call_common)
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 BEGIN_FTR_SECTION
 	extrdi.	r10, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */
 	bne	.Ltabort_syscall
 END_FTR_SECTION_IFSET(CPU_FTR_TM)
 #endif
-_ASM_NOKPROBE_SYMBOL(system_call_common)
 	mr	r10,r1
 	ld	r1,PACAKSAVE(r13)
 	std	r10,0(r1)
@@ -138,6 +296,7 @@ END_BTB_FLUSH_SECTION
 
 .Lsyscall_exit:
 	addi    r4,r1,STACK_FRAME_OVERHEAD
+	li	r5,0 /* !scv */
 	bl	syscall_exit_prepare
 
 	ld	r2,_CCR(r1)
@@ -224,10 +383,18 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	b	.	/* prevent speculative execution */
 #endif
 
+#ifdef CONFIG_PPC_BOOK3S
+_GLOBAL(ret_from_fork_scv)
+	bl	schedule_tail
+	REST_NVGPRS(r1)
+	li	r3,0	/* fork() return value */
+	b	.Lsyscall_vectored_common_exit
+#endif
+
 _GLOBAL(ret_from_fork)
 	bl	schedule_tail
 	REST_NVGPRS(r1)
-	li	r3,0
+	li	r3,0	/* fork() return value */
 	b	.Lsyscall_exit
 
 _GLOBAL(ret_from_kernel_thread)