Commit d0488597 authored by Will Deacon's avatar Will Deacon Committed by Catalin Marinas
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arm64: head: fix cache flushing and barriers in set_cpu_boot_mode_flag



set_cpu_boot_mode_flag is used to identify which exception levels are
encountered across the system by CPUs trying to enter the kernel. The
basic algorithm is: if a CPU is booting at EL2, it will set a flag at
an offset of #4 from __boot_cpu_mode, a cacheline-aligned variable.
Otherwise, a flag is set at an offset of zero into the same cacheline.
This enables us to check that all CPUs booted at the same exception
level.

This cacheline is written with the stage-1 MMU off (that is, via a
strongly-ordered mapping) and will bypass any clean lines in the cache,
leading to potential coherence problems when the variable is later
checked via the normal, cacheable mapping of the kernel image.

This patch reworks the broken flushing code so that we:

  (1) Use a DMB to order the strongly-ordered write of the cacheline
      against the subsequent cache-maintenance operation (by-VA
      operations only hazard against normal, cacheable accesses).

  (2) Use a single dc ivac instruction to invalidate any clean lines
      containing a stale copy of the line after it has been updated.
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent be6209a6
......@@ -230,11 +230,9 @@ ENTRY(set_cpu_boot_mode_flag)
cmp w20, #BOOT_CPU_MODE_EL2
b.ne 1f
add x1, x1, #4
1: dc cvac, x1 // Clean potentially dirty cache line
dsb sy
str w20, [x1] // This CPU has booted in EL1
dc civac, x1 // Clean&invalidate potentially stale cache line
dsb sy
1: str w20, [x1] // This CPU has booted in EL1
dmb sy
dc ivac, x1 // Invalidate potentially stale cache line
ret
ENDPROC(set_cpu_boot_mode_flag)
......
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