From: Catalin Marinas <catalin.marinas@arm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
Gregory CLEMENT <gregory.clement@bootlin.com>,
Russell King <linux@armlinux.org.uk>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v2 4/6] ARM: mm: Aligned pte allocation to one page
Date: Fri, 12 Jun 2020 11:25:16 +0100 [thread overview]
Message-ID: <20200612102516.GB4180@gaia> (raw)
In-Reply-To: <CAK8P3a2-g9ZmFiWJ_i4-0C6=WwzC1UjHGzY07w4y=0O1pHSX5Q@mail.gmail.com>
On Fri, Jun 12, 2020 at 10:37:15AM +0200, Arnd Bergmann wrote:
> On Thu, Jun 11, 2020 at 3:49 PM Gregory CLEMENT
> <gregory.clement@bootlin.com> wrote:
> > In pte_offset_kernel() the pte_index macro is used. This macro makes
> > the assumption that the address is aligned to a page size.
> >
> > In arm_pte_allocation, the size allocated is the size needed for 512
> > entries. Actually this size was calculated to fit in a 4K page. When
> > using larger page, the size of the table allocated is no more
> > aligned which end to give a wrong physical address.
> >
> > The solution is to round up the allocation to a page size instead of
> > the exact size of the tables (which is 4KB). It allows to comply with
> > the assumption of pte_index() but the drawback is a waste of memory
> > for the early allocation if page size is bigger than 4KB.
>
> Have you considered increasing PTRS_PER_PTE instead to fill up
> a logical page instead? If that doesn't work, can you explain here
> why not?
From what I remember, increasing the PTRS_PER_PTE also requires changing
the pgd_t array to cover them. As a side-effect, {PMD,PGDIR}_SHIFT would
need to increase. cpu_v7_set_pte_ext() also needs to take care of the
software pte offset (hard-coded at 2048 now).
Many years ago I had some patches to get rid of the software pte offset
but it wasn't really worth the maintenance hassle (only possible for
ARMv6/7). I'm not even sure it's feasible now if we gained more L_PTE_*
bits in the meantime.
--
Catalin
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next prev parent reply other threads:[~2020-06-12 10:25 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-11 13:49 [PATCH v2 0/6] ARM: Add support for large kernel page (from 8K to 64K) Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 1/6] ARM: Use PAGE_SIZE for ELF_EXEC_PAGESIZE Gregory CLEMENT
2020-06-12 8:22 ` Arnd Bergmann
2020-06-12 8:35 ` Russell King - ARM Linux admin
2020-06-12 8:46 ` Arnd Bergmann
2020-06-12 8:50 ` Russell King - ARM Linux admin
2020-06-12 11:50 ` Catalin Marinas
2020-06-12 12:06 ` Gregory CLEMENT
2020-06-12 8:52 ` Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 2/6] ARM: pagetable: prepare hardware page table to use large page Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 3/6] ARM: Make the number of fix bitmap depend on the page size Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 4/6] ARM: mm: Aligned pte allocation to one page Gregory CLEMENT
2020-06-12 8:37 ` Arnd Bergmann
2020-06-12 10:25 ` Catalin Marinas [this message]
2020-06-12 11:56 ` Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 5/6] ARM: Add large kernel page support Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 6/6] ARM: Add 64K page support at MMU level Gregory CLEMENT
2020-06-11 16:21 ` [PATCH v2 0/6] ARM: Add support for large kernel page (from 8K to 64K) Russell King - ARM Linux admin
2020-06-12 9:15 ` Gregory CLEMENT
2020-06-12 9:23 ` Arnd Bergmann
2020-06-12 12:21 ` Catalin Marinas
2020-06-12 12:49 ` Arnd Bergmann
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