[PATCH] arm64: mm: Optimise tlb flush logic where we have >4K granule

[Will Deacon]

Hi Steve,

On Fri, May 02, 2014 at 10:01:43AM +0100, Steve Capper wrote:
> The tlb maintainence functions: __cpu_flush_user_tlb_range and
> __cpu_flush_kern_tlb_range do not take into consideration the page
> granule when looping through the address range, and repeatedly flush
> tlb entries for the same page when operating with 64K pages.
> 
> This patch re-works the logic s.t. we instead advance the loop by
>  1 << (PAGE_SHIFT - 12), so avoid repeating ourselves.
> 
> Also the routines have been converted from assembler to static inline
> functions to aid with legibility and potential compiler optimisations.
> 
> Signed-off-by: Steve Capper <steve.capper at linaro.org>
> ---
> Hello,
> Options have been added to the dsbs in this patch. At the moment the
> dsb macro ignores the option, but this is set to change in future.
> 
> As always comments/critique/testers welcome!

This is likely to conflict with some barrier re-work I'm doing, but the
conflict will be trivial (and I'll probably be the guy fixing it up anyway
:).

One other comment below...

> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index 8b48203..7881d7d 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -98,11 +98,31 @@ static inline void flush_tlb_page(struct vm_area_struct *vma,
>  	dsb();
>  }
>  
> -/*
> - * Convert calls to our calling convention.
> - */
> -#define flush_tlb_range(vma,start,end)	__cpu_flush_user_tlb_range(start,end,vma)
> -#define flush_tlb_kernel_range(s,e)	__cpu_flush_kern_tlb_range(s,e)
> +static inline void flush_tlb_range(struct vm_area_struct *vma,
> +					unsigned long start, unsigned long end)
> +{
> +	unsigned long asid = (unsigned long)ASID(vma->vm_mm) << 48;
> +	unsigned long addr;
> +	start = asid | (start >> 12);
> +	end = asid | (end >> 12);
> +
> +	dsb(ishst);
> +	for (addr = start; addr < end; addr += 1 << (PAGE_SHIFT - 12))
> +		asm("tlbi vae1is, %0" : : "r"(addr));
> +	dsb(ish);
> +}
> +
> +static inline void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> +{
> +	unsigned long addr;
> +	start >>= 12;
> +	end >>= 12;
> +
> +	dsb(ishst);
> +	for (addr = start; addr < end; addr += 1 << (PAGE_SHIFT - 12))
> +		asm("tlbi vaae1is, %0" : : "r"(addr));
> +	dsb(ish);

Why have you removed the isb() here? There's not a guaranteed exception
return back to kernel text, so you could argue that it's needed. That
said, when do we actually remap kernel text? Modules are one place, but
then there's already I-side flushing (with an isb) associated with that.

Assuming that logic works out:

  Acked-by: Will Deacon <will.deacon at arm.com>

Will

> diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
> index b51d364..3ecb56c 100644
> --- a/arch/arm64/mm/Makefile
> +++ b/arch/arm64/mm/Makefile
> @@ -1,5 +1,5 @@
>  obj-y				:= dma-mapping.o extable.o fault.o init.o \
>  				   cache.o copypage.o flush.o \
>  				   ioremap.o mmap.o pgd.o mmu.o \
> -				   context.o tlb.o proc.o
> +				   context.o proc.o
>  obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
> diff --git a/arch/arm64/mm/tlb.S b/arch/arm64/mm/tlb.S
> deleted file mode 100644
> index 19da91e..0000000
> --- a/arch/arm64/mm/tlb.S
> +++ /dev/null
> @@ -1,71 +0,0 @@
> -/*
> - * Based on arch/arm/mm/tlb.S
> - *
> - * Copyright (C) 1997-2002 Russell King
> - * Copyright (C) 2012 ARM Ltd.
> - * Written by Catalin Marinas <catalin.marinas at arm.com>
> - *
> - * This program is free software; you can redistribute it and/or modify
> - * it under the terms of the GNU General Public License version 2 as
> - * published by the Free Software Foundation.
> - *
> - * This program is distributed in the hope that it will be useful,
> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> - * GNU General Public License for more details.
> - *
> - * You should have received a copy of the GNU General Public License
> - * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> - */
> -#include <linux/linkage.h>
> -#include <asm/assembler.h>
> -#include <asm/asm-offsets.h>
> -#include <asm/page.h>
> -#include <asm/tlbflush.h>
> -#include "proc-macros.S"
> -
> -/*
> - *	__cpu_flush_user_tlb_range(start, end, vma)
> - *
> - *	Invalidate a range of TLB entries in the specified address space.
> - *
> - *	- start - start address (may not be aligned)
> - *	- end   - end address (exclusive, may not be aligned)
> - *	- vma   - vma_struct describing address range
> - */
> -ENTRY(__cpu_flush_user_tlb_range)
> -	vma_vm_mm x3, x2			// get vma->vm_mm
> -	mmid	w3, x3				// get vm_mm->context.id
> -	dsb	sy
> -	lsr	x0, x0, #12			// align address
> -	lsr	x1, x1, #12
> -	bfi	x0, x3, #48, #16		// start VA and ASID
> -	bfi	x1, x3, #48, #16		// end VA and ASID
> -1:	tlbi	vae1is, x0			// TLB invalidate by address and ASID
> -	add	x0, x0, #1
> -	cmp	x0, x1
> -	b.lo	1b
> -	dsb	sy
> -	ret
> -ENDPROC(__cpu_flush_user_tlb_range)
> -
> -/*
> - *	__cpu_flush_kern_tlb_range(start,end)
> - *
> - *	Invalidate a range of kernel TLB entries.
> - *
> - *	- start - start address (may not be aligned)
> - *	- end   - end address (exclusive, may not be aligned)
> - */
> -ENTRY(__cpu_flush_kern_tlb_range)
> -	dsb	sy
> -	lsr	x0, x0, #12			// align address
> -	lsr	x1, x1, #12
> -1:	tlbi	vaae1is, x0			// TLB invalidate by address
> -	add	x0, x0, #1
> -	cmp	x0, x1
> -	b.lo	1b
> -	dsb	sy
> -	isb
> -	ret
> -ENDPROC(__cpu_flush_kern_tlb_range)
> -- 
> 1.8.1.4
> 
> 
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