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Date: Thu, 17 Sep 2015 18:23:23 +0100
From: Steve Capper <steve.capper@...aro.org>
To: Jeremy Linton <jeremy.linton@....com>
Cc: "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Steve Capper <steve.capper@....com>,
Catalin Marinas <catalin.marinas@....com>, dwoods@...ip.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Will Deacon <will.deacon@....com>, shijie.huang@....com
Subject: Re: [PATCH 7/7] arm64: Mark kernel page ranges contiguous
Hi Jeremy,
One quick comment for now below.
I ran into a problem testing this on my Seattle board, and needed the fix below.
Cheers,
--
Steve
On 16 September 2015 at 20:03, Jeremy Linton <jeremy.linton@....com> wrote:
> With 64k pages, the next larger segment size is 512M. The linux
> kernel also uses different protection flags to cover its code and data.
> Because of this requirement, the vast majority of the kernel code and
> data structures end up being mapped with 64k pages instead of the larger
> pages common with a 4k page kernel.
>
> Recent ARM processors support a contiguous bit in the
> page tables which allows the a TLB to cover a range larger than a
> single PTE if that range is mapped into physically contiguous
> ram.
>
> So, for the kernel its a good idea to set this flag. Some basic
> micro benchmarks show it can significantly reduce the number of
> L1 dTLB refills.
>
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
> arch/arm64/mm/mmu.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 62 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 9211b85..c7abbcc 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -80,19 +80,55 @@ static void split_pmd(pmd_t *pmd, pte_t *pte)
> do {
> /*
> * Need to have the least restrictive permissions available
> - * permissions will be fixed up later
> + * permissions will be fixed up later. Default the new page
> + * range as contiguous ptes.
> */
> - set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
> + set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC_CONT));
> pfn++;
> } while (pte++, i++, i < PTRS_PER_PTE);
> }
>
> +/*
> + * Given a PTE with the CONT bit set, determine where the CONT range
> + * starts, and clear the entire range of PTE CONT bits.
> + */
> +static void clear_cont_pte_range(pte_t *pte, unsigned long addr)
> +{
> + int i;
> +
> + pte -= CONT_RANGE_OFFSET(addr);
> + for (i = 0; i < CONT_RANGE; i++) {
> + set_pte(pte, pte_mknoncont(*pte));
> + pte++;
> + }
> + flush_tlb_all();
> +}
> +
> +/*
> + * Given a range of PTEs set the pfn and provided page protection flags
> + */
> +static void __populate_init_pte(pte_t *pte, unsigned long addr,
> + unsigned long end, phys_addr_t phys,
> + pgprot_t prot)
> +{
> + unsigned long pfn = __phys_to_pfn(phys);
> +
> + do {
> + /* clear all the bits except the pfn, then apply the prot */
> + set_pte(pte, pfn_pte(pfn, prot));
> + pte++;
> + pfn++;
> + addr += PAGE_SIZE;
> + } while (addr != end);
> +}
> +
> static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
> - unsigned long end, unsigned long pfn,
> + unsigned long end, phys_addr_t phys,
> pgprot_t prot,
> void *(*alloc)(unsigned long size))
> {
> pte_t *pte;
> + unsigned long next;
>
> if (pmd_none(*pmd) || pmd_sect(*pmd)) {
> pte = alloc(PTRS_PER_PTE * sizeof(pte_t));
> @@ -105,9 +141,28 @@ static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
>
> pte = pte_offset_kernel(pmd, addr);
> do {
> - set_pte(pte, pfn_pte(pfn, prot));
> - pfn++;
> - } while (pte++, addr += PAGE_SIZE, addr != end);
> + next = min(end, (addr + CONT_SIZE) & CONT_MASK);
> + if (((addr | next | phys) & CONT_RANGE_MASK) == 0) {
> + /* a block of CONT_RANGE_SIZE PTEs */
> + __populate_init_pte(pte, addr, next, phys,
> + prot | __pgprot(PTE_CONT));
> + pte += CONT_RANGE;
> + } else {
> + /*
> + * If the range being split is already inside of a
> + * contiguous range but this PTE isn't going to be
> + * contiguous, then we want to unmark the adjacent
> + * ranges, then update the portion of the range we
> + * are interrested in.
> + */
> + clear_cont_pte_range(pte, addr);
> + __populate_init_pte(pte, addr, next, phys, prot);
> + pte += CONT_RANGE_OFFSET(next - addr);
I think this should instead be:
pte += (next - addr) >> PAGE_SHIFT;
Without the above change, I get panics on boot with my Seattle board
when efi_rtc is initialised.
(I think the EFI runtime stuff exacerbates the non-contiguous code
path hence I notice it on my system).
> + }
> +
> + phys += next - addr;
> + addr = next;
> + } while (addr != end);
> }
>
> void split_pud(pud_t *old_pud, pmd_t *pmd)
> @@ -168,8 +223,7 @@ static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
> }
> }
> } else {
> - alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
> - prot, alloc);
> + alloc_init_pte(pmd, addr, next, phys, prot, alloc);
> }
> phys += next - addr;
> } while (pmd++, addr = next, addr != end);
> --
> 2.4.3
>
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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