Re: [PATCH 0/5] arm64: assorted fixes for dcache_by_line_op

[Robin Murphy]

Hi Will,

On 07/12/2018 17:53, Will Deacon wrote:
> Hi Ard,
>
> Cheers for looking at this.
>
> On Thu, Dec 06, 2018 at 04:57:34PM +0100, Ard Biesheuvel wrote:
> > This fixes two issues in dcache_by_line_op: patch #4 fixes the logic
> > that is applied when patching DC CVAP instructions, and patch #5 gets
> > rid of some unintended undefined symbols resulting from incorrect use
> > of conditional GAS directives.
> >
> > Patches #1 to #3 are groundwork for #4.
> >
> > Cc: Robin Murphy <robin.murphy@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> > Cc: Suzuki Poulose <suzuki.poulose@xxxxxxx>
> > Cc: Dave Martin <Dave.Martin@xxxxxxx>
> >
> > Ard Biesheuvel (5):
> >    arm64/alternative_cb: move callback reference into replacements
> >      section
> >    arm64/alternative_cb: add nr_alts parameter to callback handlers
> >    arm64/alternative_cb: add support for alternative sequences
> >    arm64/assembler: use callback to 3-way alt-patch DC CVAP instructions
> >    arm64/mm: use string comparisons in dcache_by_line_op
> >
> >   arch/arm64/include/asm/alternative.h | 54 +++++++++++---------
> >   arch/arm64/include/asm/assembler.h   | 17 +++---
> >   arch/arm64/include/asm/kvm_mmu.h     |  4 +-
> >   arch/arm64/kernel/alternative.c      | 22 +++++---
> >   arch/arm64/kernel/cpu_errata.c       | 24 ++++++---
> >   arch/arm64/kvm/va_layout.c           |  8 +--
> >   6 files changed, 79 insertions(+), 50 deletions(-)
>
> Whilst I can see that this solves the problem, I do wonder whether the
> additional infrastructure is really worth it. Couldn't we just do something
> really simple like the diff below instead?

Given that there's really only one place we expect CVAP to be used, I 
reckon we could factor that out beforehand to make life even simpler, as 
below.

Robin.

----->8-----
diff --git a/arch/arm64/include/asm/assembler.h 
b/arch/arm64/include/asm/assembler.h
index 6142402c2eb4..8d88d3f1e90e 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -390,11 +390,7 @@ alternative_else
 	dc	civac, \kaddr
 alternative_endif
 	.elseif	(\op == cvap)
-alternative_if ARM64_HAS_DCPOP
 	sys 3, c7, c12, 1, \kaddr	// dc cvap
-alternative_else
-	dc	cvac, \kaddr
-alternative_endif
 	.else
 	dc	\op, \kaddr
 	.endif
diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
index 0c22ede52f90..98b17bee4f9d 100644
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -212,6 +212,9 @@ ENDPROC(__dma_clean_area)
  *	- size    - size in question
  */
 ENTRY(__clean_dcache_area_pop)
+	alternative_if_not ARM64_HAS_DCPOP
+	b __clean_dcache_area_poc
+	alternative_else_nop_endif
 	dcache_by_line_op cvap, sy, x0, x1, x2, x3
 	ret
 ENDPIPROC(__clean_dcache_area_pop)
-----8<----

> Will
>
> --->8
>
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index 953208267252..8dea015b6599 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -390,27 +390,38 @@ alternative_endif
>    * 	size:		size of the region
>    * 	Corrupts:	kaddr, size, tmp1, tmp2
>    */
> +	.macro __dcache_op_workaround_clean_cache, op, kaddr
> +alternative_if_not ARM64_WORKAROUND_CLEAN_CACHE
> +	dc	\op, \kaddr
> +alternative_else
> +	dc	civac, \kaddr
> +alternative_endif
> +	.endm
> +
>   	.macro dcache_by_line_op op, domain, kaddr, size, tmp1, tmp2
>   	dcache_line_size \tmp1, \tmp2
>   	add	\size, \kaddr, \size
>   	sub	\tmp2, \tmp1, #1
>   	bic	\kaddr, \kaddr, \tmp2
>   9998:
> -	.if	(\op == cvau || \op == cvac)
> -alternative_if_not ARM64_WORKAROUND_CLEAN_CACHE
> -	dc	\op, \kaddr
> -alternative_else
> -	dc	civac, \kaddr
> -alternative_endif
> -	.elseif	(\op == cvap)
> +	.ifc	\op, cvau
> +	__dcache_op_workaround_clean_cache \op, \kaddr
> +	.else
> +	.ifc	\op, cvac
> +	__dcache_op_workaround_clean_cache \op, \kaddr
> +	.else
> +	.ifc	\op, cvap
>   alternative_if ARM64_HAS_DCPOP
>   	sys 3, c7, c12, 1, \kaddr	// dc cvap
> -alternative_else
> -	dc	cvac, \kaddr
> -alternative_endif
> +	b	9996f
> +alternative_else_nop_endif
> +	__dcache_op_workaround_clean_cache cvac, \kaddr
> +9996:
>   	.else
>   	dc	\op, \kaddr
>   	.endif
> +	.endif
> +	.endif
>   	add	\kaddr, \kaddr, \tmp1
>   	cmp	\kaddr, \size
>   	b.lo	9998b