From: Joerg Roedel <jroedel@suse.de>
To: Pekka Enberg <penberg@kernel.org>
Cc: linux-riscv <linux-riscv@lists.infradead.org>,
Palmer Dabbelt <palmer@dabbelt.com>
Subject: Re: vmalloc faulting on RISC-V
Date: Wed, 9 Sep 2020 20:28:34 +0200 [thread overview]
Message-ID: <20200909182834.GF23826@suse.de> (raw)
In-Reply-To: <CAOJsxLFWbV6FoEgHPHVN3PksrP5mXWbbFUuzH8YEDd1VdvEp7g@mail.gmail.com>
On Wed, Sep 09, 2020 at 09:29:10AM +0300, Pekka Enberg wrote:
> Why does RISC-V need vmalloc faulting in do_page_fault()? If I
> understand correctly, some architectures implement it because process
> page tables can get out of sync with "init_mm.pgd". How does that
> happen on RISC-V?
>
> I am asking because Joerg Roedel recently switched the x86
> architecture to a different approach because apparently vmalloc
> faulting is error-prone:
>
> commit 7f0a002b5a21302d9f4b29ba83c96cd433ff3769
> Author: Joerg Roedel <jroedel@suse.de>
> Date: Mon Jun 1 21:52:40 2020 -0700
>
> x86/mm: remove vmalloc faulting
>
> Remove fault handling on vmalloc areas, as the vmalloc code now takes
> care of synchronizing changes to all page-tables in the system.
It is actually not vmalloc-faulting alone that was error-prone, it was
its combination with the (now removed) vmalloc_sync_* interfaces which
had to be called at random places in the kernel. This interface was
removed and replaced by arch_sync_kernel_mappings(), which makes sure
that mappings are synchronized to all page-tables before the vmalloc'ed
pointer is returned.
Above commit to remove vmalloc-faulting on x86 had to be (partially)
reverted, because relying on arch_sync_kernel_mappings() alone turned
out to have a race condition.
Please see commit
4819e15f740e x86/mm/32: Bring back vmalloc faulting on x86_32
for details on that.
Regards,
Joerg
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next prev parent reply other threads:[~2020-09-09 18:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-09 6:29 vmalloc faulting on RISC-V Pekka Enberg
2020-09-09 18:28 ` Joerg Roedel [this message]
2020-09-09 20:35 ` Palmer Dabbelt
2020-09-18 12:08 ` Joerg Roedel
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