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From: Christoph Hellwig <hch@lst.de>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Christoph Hellwig <hch@lst.de>, Nick Hu <nickhu@andestech.com>,
	Greentime Hu <green.hu@gmail.com>,
	Vincent Chen <deanbo422@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Linux-Arch <linux-arch@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/6] uaccess: add force_uaccess_{begin,end} helpers
Date: Tue, 14 Jul 2020 09:12:11 +0200	[thread overview]
Message-ID: <20200714071211.GC776@lst.de> (raw)
In-Reply-To: <CAMuHMdUCmEeU0G9wkUxZKm5tC9YoB-KXSSCLKwpSia746Myebw@mail.gmail.com>

On Mon, Jul 13, 2020 at 03:19:42PM +0200, Geert Uytterhoeven wrote:
> > This used to set KERNEL_DS, and now it sets USER_DS, which looks wrong
> > superficially.
> 
> Thanks for noticing, and sorry for missing that myself.
> 
> The same issue is present for SuperH:
> 
>     -               set_fs(KERNEL_DS);
>     +               oldfs = force_uaccess_begin();
> 
> So the patch description should be:
> 
>     "Add helpers to wraper the get_fs/set_fs magic for undoing any damage
>      done by set_fs(USER_DS)."
> 
> and leave alone users setting KERNEL_DS?

Yes, this was broken.  Fixed for the next version.

> > If the new behaviour is fine it suggests that the old behaviour was
> > wrong, or that this is superfluous and could go entirely.
> >
> > Geert?
> 
> Nope, on m68k, TLB cache operations operate on the current address space.
> Hence to flush a kernel TLB entry, you have to switch to KERNEL_DS first.
> 
> If we're guaranteed to be already using KERNEL_DS, I guess the
> address space handling can be removed.  But can we be sure?

We can't be sure yet.  But with a lot of my pending work we should be
able to get there in the not too far future.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Linux-Arch <linux-arch@vger.kernel.org>,
	Nick Hu <nickhu@andestech.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Greentime Hu <green.hu@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vincent Chen <deanbo422@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 5/6] uaccess: add force_uaccess_{begin,end} helpers
Date: Tue, 14 Jul 2020 09:12:11 +0200	[thread overview]
Message-ID: <20200714071211.GC776@lst.de> (raw)
In-Reply-To: <CAMuHMdUCmEeU0G9wkUxZKm5tC9YoB-KXSSCLKwpSia746Myebw@mail.gmail.com>

On Mon, Jul 13, 2020 at 03:19:42PM +0200, Geert Uytterhoeven wrote:
> > This used to set KERNEL_DS, and now it sets USER_DS, which looks wrong
> > superficially.
> 
> Thanks for noticing, and sorry for missing that myself.
> 
> The same issue is present for SuperH:
> 
>     -               set_fs(KERNEL_DS);
>     +               oldfs = force_uaccess_begin();
> 
> So the patch description should be:
> 
>     "Add helpers to wraper the get_fs/set_fs magic for undoing any damage
>      done by set_fs(USER_DS)."
> 
> and leave alone users setting KERNEL_DS?

Yes, this was broken.  Fixed for the next version.

> > If the new behaviour is fine it suggests that the old behaviour was
> > wrong, or that this is superfluous and could go entirely.
> >
> > Geert?
> 
> Nope, on m68k, TLB cache operations operate on the current address space.
> Hence to flush a kernel TLB entry, you have to switch to KERNEL_DS first.
> 
> If we're guaranteed to be already using KERNEL_DS, I guess the
> address space handling can be removed.  But can we be sure?

We can't be sure yet.  But with a lot of my pending work we should be
able to get there in the not too far future.

_______________________________________________
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linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  reply	other threads:[~2020-07-14  7:12 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-10 13:57 clean up address limit helpers Christoph Hellwig
2020-07-10 13:57 ` Christoph Hellwig
2020-07-10 13:57 ` [PATCH 1/6] syscalls: use uaccess_kernel in addr_limit_user_check Christoph Hellwig
2020-07-10 13:57   ` Christoph Hellwig
2020-07-10 13:57 ` [PATCH 2/6] nds32: use uaccess_kernel in show_regs Christoph Hellwig
2020-07-10 13:57   ` Christoph Hellwig
2020-07-13 10:02   ` Greentime Hu
2020-07-13 10:02     ` Greentime Hu
2020-07-10 13:57 ` [PATCH 3/6] riscv: include <asm/pgtable.h> in <asm/uaccess.h> Christoph Hellwig
2020-07-10 13:57   ` Christoph Hellwig
2020-07-21 23:02   ` Palmer Dabbelt
2020-07-21 23:02     ` Palmer Dabbelt
2020-07-10 13:57 ` [PATCH 4/6] uaccess: remove segment_eq Christoph Hellwig
2020-07-10 13:57   ` Christoph Hellwig
2020-07-13  9:16   ` Geert Uytterhoeven
2020-07-13  9:16     ` Geert Uytterhoeven
2020-07-13 10:05   ` Greentime Hu
2020-07-13 10:05     ` Greentime Hu
2020-07-10 13:57 ` [PATCH 5/6] uaccess: add force_uaccess_{begin,end} helpers Christoph Hellwig
2020-07-10 13:57   ` Christoph Hellwig
2020-07-13  9:12   ` Geert Uytterhoeven
2020-07-13  9:12     ` Geert Uytterhoeven
2020-07-13 10:06   ` Greentime Hu
2020-07-13 10:06     ` Greentime Hu
2020-07-13 12:21   ` Mark Rutland
2020-07-13 12:21     ` Mark Rutland
2020-07-13 13:19     ` Geert Uytterhoeven
2020-07-13 13:19       ` Geert Uytterhoeven
2020-07-13 13:19       ` Geert Uytterhoeven
2020-07-14  7:12       ` Christoph Hellwig [this message]
2020-07-14  7:12         ` Christoph Hellwig
2020-07-13 12:26   ` Mark Rutland
2020-07-13 12:26     ` Mark Rutland
2020-07-10 13:57 ` [PATCH 6/6] exec: use force_uaccess_begin during exec and exit Christoph Hellwig
2020-07-10 13:57   ` Christoph Hellwig
2020-07-10 15:25 ` clean up address limit helpers Linus Torvalds
2020-07-10 15:25   ` Linus Torvalds
2020-07-14  7:09   ` Christoph Hellwig
2020-07-14  7:09     ` Christoph Hellwig
2020-07-14 15:33     ` Linus Torvalds
2020-07-14 15:33       ` Linus Torvalds
  -- strict thread matches above, loose matches on Subject: below --
2020-07-14 10:54 clean up address limit helpers v2 Christoph Hellwig
2020-07-14 10:55 ` [PATCH 5/6] uaccess: add force_uaccess_{begin,end} helpers Christoph Hellwig
2020-07-14 10:55   ` Christoph Hellwig
2020-07-14 15:29   ` Linus Torvalds
2020-07-14 15:29     ` Linus Torvalds

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