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Commit 3b714275 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
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arm64: convert native/compat syscall entry to C 



Now that the syscall invocation logic is in C, we can migrate the rest
of the syscall entry logic over, so that the entry assembly needn't look
at the register values at all.

The SVE reset across syscall logic now unconditionally clears TIF_SVE,
but sve_user_disable() will only write back to CPACR_EL1 when SVE is
actually enabled.

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Reviewed-by: default avatarDave Martin <dave.martin@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent f37099b6

arch/arm64/include/asm/syscall.h

+4 −0
Original line number Diff line number Diff line
@@ -26,6 +26,10 @@ typedef long (*syscall_fn_t)(unsigned long, unsigned long, 


extern const syscall_fn_t sys_call_table[];



#ifdef CONFIG_COMPAT

extern const syscall_fn_t compat_sys_call_table[];

#endif



static inline int syscall_get_nr(struct task_struct *task,

				 struct pt_regs *regs)

{

arch/arm64/kernel/entry.S

+4 −38
Original line number Diff line number Diff line
@@ -720,14 +720,9 @@ el0_sync_compat: 
	b.ge	el0_dbg

	b	el0_inv

el0_svc_compat:

	/*

	 * AArch32 syscall handling

	 */

	ldr	x16, [tsk, #TSK_TI_FLAGS]	// load thread flags

	adrp	stbl, compat_sys_call_table	// load compat syscall table pointer

	mov	wscno, w7			// syscall number in w7 (r7)

	mov     wsc_nr, #__NR_compat_syscalls

	b	el0_svc_naked

	mov	x0, sp

	bl	el0_svc_compat_handler

	b	ret_to_user



	.align	6

el0_irq_compat:
@@ -925,37 +920,8 @@ ENDPROC(ret_to_user) 
 */

	.align	6

el0_svc:

	ldr	x16, [tsk, #TSK_TI_FLAGS]	// load thread flags

	adrp	stbl, sys_call_table		// load syscall table pointer

	mov	wscno, w8			// syscall number in w8

	mov	wsc_nr, #__NR_syscalls



#ifdef CONFIG_ARM64_SVE

alternative_if_not ARM64_SVE

	b	el0_svc_naked

alternative_else_nop_endif

	tbz	x16, #TIF_SVE, el0_svc_naked	// Skip unless TIF_SVE set:

	bic	x16, x16, #_TIF_SVE		// discard SVE state

	str	x16, [tsk, #TSK_TI_FLAGS]



	/*

	 * task_fpsimd_load() won't be called to update CPACR_EL1 in

	 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only

	 * happens if a context switch or kernel_neon_begin() or context

	 * modification (sigreturn, ptrace) intervenes.

	 * So, ensure that CPACR_EL1 is already correct for the fast-path case:

	 */

	mrs	x9, cpacr_el1

	bic	x9, x9, #CPACR_EL1_ZEN_EL0EN	// disable SVE for el0

	msr	cpacr_el1, x9			// synchronised by eret to el0

#endif



el0_svc_naked:					// compat entry point

	mov	x0, sp

	mov	w1, wscno

	mov	w2, wsc_nr

	mov	x3, stbl

	bl	el0_svc_common

	bl	el0_svc_handler

	b	ret_to_user

ENDPROC(el0_svc)

arch/arm64/kernel/syscall.c

+35 −2
Original line number Diff line number Diff line
@@ -8,8 +8,10 @@ 
#include <linux/syscalls.h>



#include <asm/daifflags.h>

#include <asm/fpsimd.h>

#include <asm/syscall.h>

#include <asm/thread_info.h>

#include <asm/unistd.h>



long compat_arm_syscall(struct pt_regs *regs);
@@ -58,7 +60,7 @@ static inline bool has_syscall_work(unsigned long flags) 
int syscall_trace_enter(struct pt_regs *regs);

void syscall_trace_exit(struct pt_regs *regs);



asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,

static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,

			   const syscall_fn_t syscall_table[])

{

	unsigned long flags = current_thread_info()->flags;
@@ -96,3 +98,34 @@ asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, 
trace_exit:

	syscall_trace_exit(regs);

}



static inline void sve_user_discard(void)

{

	if (!system_supports_sve())

		return;



	clear_thread_flag(TIF_SVE);



	/*

	 * task_fpsimd_load() won't be called to update CPACR_EL1 in

	 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only

	 * happens if a context switch or kernel_neon_begin() or context

	 * modification (sigreturn, ptrace) intervenes.

	 * So, ensure that CPACR_EL1 is already correct for the fast-path case.

	 */

	sve_user_disable();

}



asmlinkage void el0_svc_handler(struct pt_regs *regs)

{

	sve_user_discard();

	el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);

}



#ifdef CONFIG_COMPAT

asmlinkage void el0_svc_compat_handler(struct pt_regs *regs)

{

	el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,

		       compat_sys_call_table);

}

#endif