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From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Will Deacon <will@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Hugh Dickins <hughd@google.com>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag
Date: Mon, 11 Jan 2021 11:25:37 -0800	[thread overview]
Message-ID: <CAHk-=whYs9XsO88iqJzN6NC=D-dp2m0oYXuOoZ=eWnvv=5OA+w@mail.gmail.com> (raw)
In-Reply-To: <20210111142402.6euyktmcnpemanf7@box>

On Mon, Jan 11, 2021 at 6:24 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> I wonder if it would be acceptable to pass down to faultaround a copy
> of vmf, so it mess with it without risking to corrupt the original one?

I'd almost prefer to split vmf into two parts: the 'this is the fault
info' part and the 'this is the fault handling state' part.

So the first one would be filled in by the actual page faulter (or
GUP) - and then be 'const' during the lookup, while the second one
would be set up by handle_mm_fault() and would contain that "this is
the current state of my fault state machine" and contain things like
that ->pte thing.

And then if somebody actually needs to pass in "modified fault state"
(ie that whole "I'm doing fault-around, so I'll use multiple
addresses") they'd never modify the address in the fault info, they'd
just pass the address as an explicit argument (like most cases already
do - the "change addr or flags in vmf" is actually already _fairly_
rare).

               Linus

WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Android Kernel Team <kernel-team@android.com>,
	Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Hugh Dickins <hughd@google.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag
Date: Mon, 11 Jan 2021 11:25:37 -0800	[thread overview]
Message-ID: <CAHk-=whYs9XsO88iqJzN6NC=D-dp2m0oYXuOoZ=eWnvv=5OA+w@mail.gmail.com> (raw)
In-Reply-To: <20210111142402.6euyktmcnpemanf7@box>

On Mon, Jan 11, 2021 at 6:24 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> I wonder if it would be acceptable to pass down to faultaround a copy
> of vmf, so it mess with it without risking to corrupt the original one?

I'd almost prefer to split vmf into two parts: the 'this is the fault
info' part and the 'this is the fault handling state' part.

So the first one would be filled in by the actual page faulter (or
GUP) - and then be 'const' during the lookup, while the second one
would be set up by handle_mm_fault() and would contain that "this is
the current state of my fault state machine" and contain things like
that ->pte thing.

And then if somebody actually needs to pass in "modified fault state"
(ie that whole "I'm doing fault-around, so I'll use multiple
addresses") they'd never modify the address in the fault info, they'd
just pass the address as an explicit argument (like most cases already
do - the "change addr or flags in vmf" is actually already _fairly_
rare).

               Linus

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-01-11 19:26 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 17:15 [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Will Deacon
2021-01-08 17:15 ` Will Deacon
2021-01-08 17:15 ` [PATCH v2 1/3] mm: Cleanup faultaround and finish_fault() codepaths Will Deacon
2021-01-08 17:15   ` Will Deacon
2021-01-11 14:26   ` Kirill A. Shutemov
2021-01-11 14:26     ` Kirill A. Shutemov
2021-01-11 14:27     ` Will Deacon
2021-01-11 14:27       ` Will Deacon
2021-01-08 17:15 ` [PATCH v2 2/3] mm: Allow architectures to request 'old' entries when prefaulting Will Deacon
2021-01-08 17:15   ` Will Deacon
2021-01-11 14:25   ` Kirill A. Shutemov
2021-01-11 14:25     ` Kirill A. Shutemov
2021-01-11 14:37     ` Will Deacon
2021-01-11 14:37       ` Will Deacon
2021-01-11 14:47       ` Kirill A. Shutemov
2021-01-11 14:47         ` Kirill A. Shutemov
2021-01-08 17:15 ` [PATCH v2 3/3] arm64: mm: Implement arch_wants_old_prefaulted_pte() Will Deacon
2021-01-08 17:15   ` Will Deacon
2021-01-08 19:34 ` [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Linus Torvalds
2021-01-08 19:34   ` Linus Torvalds
2021-01-08 19:34   ` Linus Torvalds
2021-01-08 19:42   ` Linus Torvalds
2021-01-08 19:42     ` Linus Torvalds
2021-01-08 19:42     ` Linus Torvalds
2021-01-11 14:01     ` Will Deacon
2021-01-11 14:01       ` Will Deacon
2021-01-11 13:30   ` Will Deacon
2021-01-11 13:30     ` Will Deacon
2021-01-11 21:03     ` Hugh Dickins
2021-01-11 21:03       ` Hugh Dickins
2021-01-11 21:03       ` Hugh Dickins
2021-01-12 21:46       ` Will Deacon
2021-01-12 21:46         ` Will Deacon
2021-01-11 14:24   ` Kirill A. Shutemov
2021-01-11 14:24     ` Kirill A. Shutemov
2021-01-11 19:25     ` Linus Torvalds [this message]
2021-01-11 19:25       ` Linus Torvalds
2021-01-11 19:25       ` Linus Torvalds
2021-01-12 21:47       ` Will Deacon
2021-01-12 21:47         ` Will Deacon
2021-01-12 21:55         ` Linus Torvalds
2021-01-12 21:55           ` Linus Torvalds
2021-01-12 21:55           ` Linus Torvalds

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