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arm64: Add support for SB barrier and patch in over DSB; ISB sequences

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We currently use a DSB; ISB sequence to inhibit speculation in set_fs().
Whilst this works for current CPUs, future CPUs may implement a new SB
barrier instruction which acts as an architected speculation barrier.

On CPUs that support it, patch in an SB; NOP sequence over the DSB; ISB
sequence and advertise the presence of the new instruction to userspace.

Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon
2018-06-14 11:21:34 +01:00
parent 0b587c84e4
commit bd4fb6d270
8 changed files with 40 additions and 3 deletions
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13
arch/arm64/include/asm/assembler.h
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@@ -122,6 +122,19 @@
hint #20
.endm
/*
* Speculation barrier
*/
.macro sb
alternative_if_not ARM64_HAS_SB
dsb nsh
isb
alternative_else
SB_BARRIER_INSN
nop
alternative_endif
.endm
/*
* Sanitise a 64-bit bounded index wrt speculation, returning zero if out
* of bounds.