Commit 3e393417 authored Jan 16, 2020 by Mark Rutland Committed by Will Deacon Jan 17, 2020

arm64: entry: cleanup sp_el0 manipulation



The kernel stashes the current task struct in sp_el0 so that this can be
acquired consistently/cheaply when required. When we take an exception
from EL0 we have to:

1) stash the original sp_el0 value
2) find the current task
3) update sp_el0 with the current task pointer

Currently steps #1 and #2 occur in one place, and step #3 a while later.
As the value of sp_el0 is immaterial between these points, let's move
them together to make the code clearer and minimize ifdeffery. This
necessitates moving the comment for MDSCR_EL1.SS.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

parent 7a2c0944

arch/arm64/kernel/entry.S

+7 −10

Original line number	Diff line number	Diff line
		@@ -167,9 +167,13 @@ alternative_cb_end
		.if \el == 0
		clear_gp_regs
		mrs x21, sp_el0
		ldr_this_cpu tsk, __entry_task, x20 // Ensure MDSCR_EL1.SS is clear,
		ldr x19, [tsk, #TSK_TI_FLAGS] // since we can unmask debug
		disable_step_tsk x19, x20 // exceptions when scheduling.
		ldr_this_cpu tsk, __entry_task, x20
		msr sp_el0, tsk

		// Ensure MDSCR_EL1.SS is clear, since we can unmask debug exceptions
		// when scheduling.
		ldr x19, [tsk, #TSK_TI_FLAGS]
		disable_step_tsk x19, x20

		apply_ssbd 1, x22, x23

		@@ -232,13 +236,6 @@ alternative_else_nop_endif
		str w21, [sp, #S_SYSCALLNO]
		.endif

		/*
		* Set sp_el0 to current thread_info.
		*/
		.if \el == 0
		msr sp_el0, tsk
		.endif

		/* Save pmr */
		alternative_if ARM64_HAS_IRQ_PRIO_MASKING
		mrs_s x20, SYS_ICC_PMR_EL1

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