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From: Ingo Molnar <mingo@kernel.org>
To: Dave Hansen <dave@sr71.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
	dave.hansen@linux.intel.com, srikar@linux.vnet.ibm.com,
	vbabka@suse.cz, kirill.shutemov@linux.intel.com,
	aarcange@redhat.com, n-horiguchi@ah.jp.nec.com, jack@suse.cz
Subject: Re: [PATCH 02/33] mm: overload get_user_pages() functions
Date: Tue, 16 Feb 2016 09:36:06 +0100	[thread overview]
Message-ID: <20160216083606.GB3335@gmail.com> (raw)
In-Reply-To: <20160212210155.73222EE1@viggo.jf.intel.com>


* Dave Hansen <dave@sr71.net> wrote:

> 
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> The concept here was a suggestion from Ingo.  The implementation
> horrors are all mine.
> 
> This allows get_user_pages(), get_user_pages_unlocked(), and
> get_user_pages_locked() to be called with or without the
> leading tsk/mm arguments.  We will give a compile-time warning
> about the old style being __deprecated and we will also
> WARN_ON() if the non-remote version is used for a remote-style
> access.

So at minimum this should be WARN_ON_ONCE(), to make it easier to recover some 
meaningful kernel log from such incidents.

But:

> Doing this, folks will get nice warnings and will not break the
> build.  This should be nice for -next and will hopefully let
> developers fix up their own code instead of maintainers needing
> to do it at merge time.
> 
> The way we do this is hideous.  It uses the __VA_ARGS__ macro
> functionality to call different functions based on the number
> of arguments passed to the macro.
> 
> There's an additional hack to ensure that our EXPORT_SYMBOL()
> of the deprecated symbols doesn't trigger a warning.
> 
> We should be able to remove this mess as soon as -rc1 hits in
> the release after this is merged.

So when I suggested this then it looked a _lot_ cleanear to me, in my head!

OTOH this, if factored out a bit perhaps, could be the basis for a useful 
technical model to do 'phased in, -next invariant' prototype migrations in the 
future, especially when it involves lots of subsystems.

Strictly only in cases where -rc1 will truly get rid of the __VA_ARGS__ hackery - 
which we'd do in this case.

Nevertheless I'd love to have a high level buy-in from either Linus or Andrew that 
we can do it this way, as the hackery looks very hideous...

The alternative would be to allow the -next churn and to allow the occasional 
(fairly trivial but tester-disruptive) build breakage.

Thanks,

	Ingo

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  reply	other threads:[~2016-02-16  8:36 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-12 21:01 [PATCH 00/33] x86: Memory Protection Keys (v10) Dave Hansen
2016-02-12 21:01 ` [PATCH 01/33] mm: introduce get_user_pages_remote() Dave Hansen
2016-02-15  6:09   ` Balbir Singh
2016-02-15 16:29     ` Dave Hansen
2016-02-15  6:14   ` Srikar Dronamraju
2016-02-12 21:01 ` [PATCH 02/33] mm: overload get_user_pages() functions Dave Hansen
2016-02-16  8:36   ` Ingo Molnar [this message]
2016-02-17 18:15     ` Dave Hansen
2016-02-12 21:01 ` [PATCH 03/33] mm, gup: switch callers of get_user_pages() to not pass tsk/mm Dave Hansen
2016-02-12 21:01 ` [PATCH 04/33] x86, fpu: add placeholder for Processor Trace XSAVE state Dave Hansen
2016-02-12 21:02 ` [PATCH 05/33] x86, pkeys: Add Kconfig option Dave Hansen
2016-02-12 21:02 ` [PATCH 06/33] x86, pkeys: cpuid bit definition Dave Hansen
2016-02-12 21:02 ` [PATCH 07/33] x86, pkeys: define new CR4 bit Dave Hansen
2016-02-12 21:02 ` [PATCH 08/33] x86, pkeys: add PKRU xsave fields and data structure(s) Dave Hansen
2016-02-12 21:02 ` [PATCH 09/33] x86, pkeys: PTE bits for storing protection key Dave Hansen
2016-02-12 21:02 ` [PATCH 10/33] x86, pkeys: new page fault error code bit: PF_PK Dave Hansen
2016-02-12 21:02 ` [PATCH 11/33] x86, pkeys: store protection in high VMA flags Dave Hansen
2016-02-12 21:02 ` [PATCH 12/33] x86, pkeys: arch-specific protection bits Dave Hansen
2016-02-12 21:02 ` [PATCH 13/33] x86, pkeys: pass VMA down in to fault signal generation code Dave Hansen
2016-02-12 21:02 ` [PATCH 14/33] signals, pkeys: notify userspace about protection key faults Dave Hansen
2016-02-12 21:02 ` [PATCH 15/33] x86, pkeys: fill in pkey field in siginfo Dave Hansen
2016-02-12 21:02 ` [PATCH 16/33] x86, pkeys: add functions to fetch PKRU Dave Hansen
2016-02-12 21:02 ` [PATCH 17/33] mm: factor out VMA fault permission checking Dave Hansen
2016-02-12 21:02 ` [PATCH 18/33] x86, mm: simplify get_user_pages() PTE bit handling Dave Hansen
2016-02-12 21:02 ` [PATCH 19/33] x86, pkeys: check VMAs and PTEs for protection keys Dave Hansen
2016-02-12 21:02 ` [PATCH 20/33] mm: do not enforce PKEY permissions on "foreign" mm access Dave Hansen
2016-02-12 21:02 ` [PATCH 21/33] x86, pkeys: optimize fault handling in access_error() Dave Hansen
2016-02-12 21:02 ` [PATCH 22/33] x86, pkeys: differentiate instruction fetches Dave Hansen
2016-02-12 21:02 ` [PATCH 23/33] x86, pkeys: dump PKRU with other kernel registers Dave Hansen
2016-02-12 21:02 ` [PATCH 24/33] x86, pkeys: dump pkey from VMA in /proc/pid/smaps Dave Hansen
2016-02-12 21:02 ` [PATCH 25/33] x86, pkeys: add Kconfig prompt to existing config option Dave Hansen
2016-02-12 21:02 ` [PATCH 26/33] x86, pkeys: actually enable Memory Protection Keys in CPU Dave Hansen
2016-02-12 21:02 ` [PATCH 27/33] mm, multi-arch: pass a protection key in to calc_vm_flag_bits() Dave Hansen
2016-02-12 21:02 ` [PATCH 28/33] x86, pkeys: add arch_validate_pkey() Dave Hansen
2016-02-12 21:02 ` [PATCH 29/33] x86: separate out LDT init from context init Dave Hansen
2016-02-12 21:02 ` [PATCH 30/33] x86, fpu: allow setting of XSAVE state Dave Hansen
2016-02-12 21:02 ` [PATCH 31/33] x86, pkeys: allow kernel to modify user pkey rights register Dave Hansen
2016-02-12 21:02 ` [PATCH 32/33] x86, pkeys: create an x86 arch_calc_vm_prot_bits() for VMA flags Dave Hansen
2016-02-12 21:02 ` [PATCH 33/33] x86, pkeys: execute-only support Dave Hansen
2016-02-17 21:27   ` Kees Cook
2016-02-17 21:33     ` Dave Hansen
2016-02-17 21:36       ` Kees Cook
2016-02-17 22:17     ` Andy Lutomirski
2016-02-17 22:53       ` Dave Hansen
2016-02-18  0:46         ` Andy Lutomirski
2016-02-16  9:29 ` [PATCH 00/33] x86: Memory Protection Keys (v10) Ingo Molnar

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