[v2,02/17] arm64/lib: copy_page: avoid x18 register in assembler code
diff mbox series

Message ID 20191024225132.13410-3-samitolvanen@google.com
State New
Headers show
Series
  • [v2,01/17] arm64: mm: don't use x18 in idmap_kpti_install_ng_mappings
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Commit Message

Sami Tolvanen Oct. 24, 2019, 10:51 p.m. UTC
From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Register x18 will no longer be used as a caller save register in the
future, so stop using it in the copy_page() code.

Link: https://patchwork.kernel.org/patch/9836869/
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/arm64/lib/copy_page.S | 38 +++++++++++++++++++-------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

Comments

Mark Rutland Oct. 25, 2019, 9:41 a.m. UTC | #1
On Thu, Oct 24, 2019 at 03:51:17PM -0700, samitolvanen@google.com wrote:
> From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> 
> Register x18 will no longer be used as a caller save register in the
> future, so stop using it in the copy_page() code.
> 
> Link: https://patchwork.kernel.org/patch/9836869/
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  arch/arm64/lib/copy_page.S | 38 +++++++++++++++++++-------------------
>  1 file changed, 19 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm64/lib/copy_page.S b/arch/arm64/lib/copy_page.S
> index bbb8562396af..8b562264c165 100644
> --- a/arch/arm64/lib/copy_page.S
> +++ b/arch/arm64/lib/copy_page.S
> @@ -34,45 +34,45 @@ alternative_else_nop_endif
>  	ldp	x14, x15, [x1, #96]
>  	ldp	x16, x17, [x1, #112]
>  
> -	mov	x18, #(PAGE_SIZE - 128)
> +	add	x0, x0, #256
>  	add	x1, x1, #128
>  1:
> -	subs	x18, x18, #128
> +	tst	x0, #(PAGE_SIZE - 1)
>  
>  alternative_if ARM64_HAS_NO_HW_PREFETCH
>  	prfm	pldl1strm, [x1, #384]
>  alternative_else_nop_endif
>  
> -	stnp	x2, x3, [x0]
> +	stnp	x2, x3, [x0, #-256]
>  	ldp	x2, x3, [x1]
> -	stnp	x4, x5, [x0, #16]
> +	stnp	x4, x5, [x0, #-240]
>  	ldp	x4, x5, [x1, #16]

For legibility, could we make the offset and bias explicit in the STNPs
so that these line up? e.g.

	stnp	x4, x5, [x0, #16 - 256]
	ldp	x4, x5, [x1, #16]

... that'd make it much easier to see by eye that this is sound, much as
I trust my mental arithmetic. ;)

> -	stnp	x6, x7, [x0, #32]
> +	stnp	x6, x7, [x0, #-224]
>  	ldp	x6, x7, [x1, #32]
> -	stnp	x8, x9, [x0, #48]
> +	stnp	x8, x9, [x0, #-208]
>  	ldp	x8, x9, [x1, #48]
> -	stnp	x10, x11, [x0, #64]
> +	stnp	x10, x11, [x0, #-192]
>  	ldp	x10, x11, [x1, #64]
> -	stnp	x12, x13, [x0, #80]
> +	stnp	x12, x13, [x0, #-176]
>  	ldp	x12, x13, [x1, #80]
> -	stnp	x14, x15, [x0, #96]
> +	stnp	x14, x15, [x0, #-160]
>  	ldp	x14, x15, [x1, #96]
> -	stnp	x16, x17, [x0, #112]
> +	stnp	x16, x17, [x0, #-144]
>  	ldp	x16, x17, [x1, #112]
>  
>  	add	x0, x0, #128
>  	add	x1, x1, #128
>  
> -	b.gt	1b
> +	b.ne	1b
>  
> -	stnp	x2, x3, [x0]
> -	stnp	x4, x5, [x0, #16]
> -	stnp	x6, x7, [x0, #32]
> -	stnp	x8, x9, [x0, #48]
> -	stnp	x10, x11, [x0, #64]
> -	stnp	x12, x13, [x0, #80]
> -	stnp	x14, x15, [x0, #96]
> -	stnp	x16, x17, [x0, #112]
> +	stnp	x2, x3, [x0, #-256]
> +	stnp	x4, x5, [x0, #-240]
> +	stnp	x6, x7, [x0, #-224]
> +	stnp	x8, x9, [x0, #-208]
> +	stnp	x10, x11, [x0, #-192]
> +	stnp	x12, x13, [x0, #-176]
> +	stnp	x14, x15, [x0, #-160]
> +	stnp	x16, x17, [x0, #-144]

... likewise here:

	stnp	xt1, xt2, [x0, #off - 256]

I don't see a nicer way to write this sequence without using an
additional register, so with those changes:

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.

>  
>  	ret
>  ENDPROC(copy_page)
> -- 
> 2.24.0.rc0.303.g954a862665-goog
>
Sami Tolvanen Oct. 25, 2019, 9:40 p.m. UTC | #2
On Fri, Oct 25, 2019 at 2:41 AM Mark Rutland <mark.rutland@arm.com> wrote:
> > diff --git a/arch/arm64/lib/copy_page.S b/arch/arm64/lib/copy_page.S
> > index bbb8562396af..8b562264c165 100644
> > --- a/arch/arm64/lib/copy_page.S
> > +++ b/arch/arm64/lib/copy_page.S
> > @@ -34,45 +34,45 @@ alternative_else_nop_endif
> >       ldp     x14, x15, [x1, #96]
> >       ldp     x16, x17, [x1, #112]
> >
> > -     mov     x18, #(PAGE_SIZE - 128)
> > +     add     x0, x0, #256
> >       add     x1, x1, #128
> >  1:
> > -     subs    x18, x18, #128
> > +     tst     x0, #(PAGE_SIZE - 1)
> >
> >  alternative_if ARM64_HAS_NO_HW_PREFETCH
> >       prfm    pldl1strm, [x1, #384]
> >  alternative_else_nop_endif
> >
> > -     stnp    x2, x3, [x0]
> > +     stnp    x2, x3, [x0, #-256]
> >       ldp     x2, x3, [x1]
> > -     stnp    x4, x5, [x0, #16]
> > +     stnp    x4, x5, [x0, #-240]
> >       ldp     x4, x5, [x1, #16]
>
> For legibility, could we make the offset and bias explicit in the STNPs
> so that these line up? e.g.
>
>         stnp    x4, x5, [x0, #16 - 256]
>         ldp     x4, x5, [x1, #16]
>
> ... that'd make it much easier to see by eye that this is sound, much as
> I trust my mental arithmetic. ;)

Sure, that makes sense. I'll change this in v3.

Sami

Patch
diff mbox series

diff --git a/arch/arm64/lib/copy_page.S b/arch/arm64/lib/copy_page.S
index bbb8562396af..8b562264c165 100644
--- a/arch/arm64/lib/copy_page.S
+++ b/arch/arm64/lib/copy_page.S
@@ -34,45 +34,45 @@  alternative_else_nop_endif
 	ldp	x14, x15, [x1, #96]
 	ldp	x16, x17, [x1, #112]
 
-	mov	x18, #(PAGE_SIZE - 128)
+	add	x0, x0, #256
 	add	x1, x1, #128
 1:
-	subs	x18, x18, #128
+	tst	x0, #(PAGE_SIZE - 1)
 
 alternative_if ARM64_HAS_NO_HW_PREFETCH
 	prfm	pldl1strm, [x1, #384]
 alternative_else_nop_endif
 
-	stnp	x2, x3, [x0]
+	stnp	x2, x3, [x0, #-256]
 	ldp	x2, x3, [x1]
-	stnp	x4, x5, [x0, #16]
+	stnp	x4, x5, [x0, #-240]
 	ldp	x4, x5, [x1, #16]
-	stnp	x6, x7, [x0, #32]
+	stnp	x6, x7, [x0, #-224]
 	ldp	x6, x7, [x1, #32]
-	stnp	x8, x9, [x0, #48]
+	stnp	x8, x9, [x0, #-208]
 	ldp	x8, x9, [x1, #48]
-	stnp	x10, x11, [x0, #64]
+	stnp	x10, x11, [x0, #-192]
 	ldp	x10, x11, [x1, #64]
-	stnp	x12, x13, [x0, #80]
+	stnp	x12, x13, [x0, #-176]
 	ldp	x12, x13, [x1, #80]
-	stnp	x14, x15, [x0, #96]
+	stnp	x14, x15, [x0, #-160]
 	ldp	x14, x15, [x1, #96]
-	stnp	x16, x17, [x0, #112]
+	stnp	x16, x17, [x0, #-144]
 	ldp	x16, x17, [x1, #112]
 
 	add	x0, x0, #128
 	add	x1, x1, #128
 
-	b.gt	1b
+	b.ne	1b
 
-	stnp	x2, x3, [x0]
-	stnp	x4, x5, [x0, #16]
-	stnp	x6, x7, [x0, #32]
-	stnp	x8, x9, [x0, #48]
-	stnp	x10, x11, [x0, #64]
-	stnp	x12, x13, [x0, #80]
-	stnp	x14, x15, [x0, #96]
-	stnp	x16, x17, [x0, #112]
+	stnp	x2, x3, [x0, #-256]
+	stnp	x4, x5, [x0, #-240]
+	stnp	x6, x7, [x0, #-224]
+	stnp	x8, x9, [x0, #-208]
+	stnp	x10, x11, [x0, #-192]
+	stnp	x12, x13, [x0, #-176]
+	stnp	x14, x15, [x0, #-160]
+	stnp	x16, x17, [x0, #-144]
 
 	ret
 ENDPROC(copy_page)