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From: Dave Martin <Dave.Martin@arm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: marc.zyngier@arm.com, catalin.marinas@arm.com,
	will.deacon@arm.com, linux-kernel@vger.kernel.org,
	linux@dominikbrodowski.net, james.morse@arm.com,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 06/18] arm64: move sve_user_{enable, disable} to <asm/fpsimd.h>
Date: Wed, 16 May 2018 10:01:32 +0100	[thread overview]
Message-ID: <20180516090121.GQ7753@e103592.cambridge.arm.com> (raw)
In-Reply-To: <20180515163352.sl7sfaswv4hsktl7@lakrids.cambridge.arm.com>

On Tue, May 15, 2018 at 05:33:52PM +0100, Mark Rutland wrote:
> On Tue, May 15, 2018 at 01:19:26PM +0100, Dave Martin wrote:
> > On Tue, May 15, 2018 at 11:39:36AM +0100, Mark Rutland wrote:
> > > On Mon, May 14, 2018 at 12:06:50PM +0100, Dave Martin wrote:
> > > > On Mon, May 14, 2018 at 10:46:28AM +0100, Mark Rutland wrote:

[...]

> > > > > @@ -107,6 +119,9 @@ static inline int sve_get_current_vl(void)
> > > > >  	return -EINVAL;
> > > > >  }
> > > > >  
> > > > > +static inline void sve_user_disable(void) { }
> > > > > +static inline void sve_user_enable(void) { }
> > > > > +
> > > > 
> > > > Alternatively, just move the full definitions outside the #ifdef
> > > > CONFIG_ARM64_SVE.
> > > 
> > > Can do, though I was trying to keep the exsting pattern with empty
> > > inlines for the !CONFIG_ARM64_SVE case.
> > 
> > There isn't really a pattern.  I tried to avoid dummy versions where
> > there's no real reason to have them.  I don't _think_ they're really
> > needed here, unless I missed something.  Did you get build failures
> > without them?
> 
> I need *some* definition so that sve_user_reset() in the syscall path
> can compile without ifdeferry. 
> 
> In sve_user_reset() I first check system_supports_sve(), which checks
> IS_ENABLED(CONFIG_ARM64_SVE), so the call should be optimised away when
> !CONFIG_ARM64_SVE, but I need a prototype regardless.

What I envisaged is that you move the real definitions outside the
#ifdef so that they're defined unconditionally, and get rid of the
dummies.

Having a dummy definition of sve_user_enable() really feels like it's
papering over something.  How could it be appropriate to call this in a
non-SVE enabled system?  You _do_ guard the call to this already, so
hiding the real function body for CONFIG_ARM64_SVE=n doesn't appear to
achieve anything.  Maybe I missed something somewhere.

A dummy sve_user_disable() is a bit more reasonable though, but we want
this to be a nop on non-SVE hardware even if CONFIG_ARM64_SVE=y.

What about moving the system_supports_sve() check inside
sve_user_disable()?

[...]

> > > Earlier I'd put BUILD_BUG() in the body for the !CONFIG_ARM64_SVE case,
> > > to catch that kind of thing -- I could restore that.
> > 
> > IIUC:
> > 
> > 	if (0) {
> > 		BUILD_BUG_ON(1);
> > 	}
> > 
> > can still fire, in which case it's futile checking for CONFIG_ARM64_SVE
> > in most of the SVE support code.
> 
> We already rely on BUILD_BUG() not firing in paths that can be trivially
> optimized away. e.g. in the cmpxchg code.

Fair enough.  I had been unsure on this point.

If you want to put a BUILD_BUG_ON(!IS_ENABLED(CONFIG_ARM64_SVE)) in
sve_user_enable() and build with CONFIG_ARM64_SVE=n to check it works,
then I'd be fine with that.

This doesn't capture the runtime part of the condition, but it's better
than nothing.

[...]

> > > > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> > > > > index 088940387a4d..79a81c7d85c6 100644
> > > > > --- a/arch/arm64/kernel/fpsimd.c
> > > > > +++ b/arch/arm64/kernel/fpsimd.c
> > > > > @@ -159,7 +159,6 @@ static void sve_free(struct task_struct *task)
> > > > >  	__sve_free(task);
> > > > >  }
> > > > >  
> > > > > -
> > > > 
> > > > Hmmm, Ack.  Check for conflicts with the KVM FPSIMD rework [1] (though
> > > > trivial).
> > > 
> > > I'll assume that Ack stands regardless. :)
> > 
> > Actually, I was just commenting on the deleted blank line... 
> 
> Ah. I've restored that now.

I meant Ack to the deletion.  It looks like the blank line was
spuriously introduced in the first place.  But it doesn't hugely matter
either way.

Cheers
---Dave

  reply	other threads:[~2018-05-16  9:01 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-14  9:46 [PATCH 00/18] arm64: invoke syscalls with pt_regs Mark Rutland
2018-05-14  9:46 ` [PATCH 01/18] arm64: consistently use unsigned long for thread flags Mark Rutland
2018-05-14  9:57   ` Dave Martin
2018-05-14  9:46 ` [PATCH 02/18] arm64: move SCTLR_EL{1,2} assertions to <asm/sysreg.h> Mark Rutland
2018-05-14 10:00   ` Dave Martin
2018-05-14 10:08     ` Mark Rutland
2018-05-14 11:20       ` Dave Martin
2018-05-14 11:56         ` Robin Murphy
2018-05-14 12:06           ` Mark Rutland
2018-05-14 12:41             ` Dave Martin
2018-05-14 13:10               ` Mark Rutland
2018-05-14  9:46 ` [PATCH 03/18] arm64: introduce sysreg_clear_set() Mark Rutland
2018-05-14 10:04   ` Dave Martin
2018-05-14  9:46 ` [PATCH 04/18] arm64: kill config_sctlr_el1() Mark Rutland
2018-05-14 10:05   ` Dave Martin
2018-05-14  9:46 ` [PATCH 05/18] arm64: kill change_cpacr() Mark Rutland
2018-05-14 10:06   ` Dave Martin
2018-05-14  9:46 ` [PATCH 06/18] arm64: move sve_user_{enable,disable} to <asm/fpsimd.h> Mark Rutland
2018-05-14 11:06   ` [PATCH 06/18] arm64: move sve_user_{enable, disable} " Dave Martin
2018-05-15 10:39     ` Mark Rutland
2018-05-15 12:19       ` Dave Martin
2018-05-15 16:33         ` Mark Rutland
2018-05-16  9:01           ` Dave Martin [this message]
2018-06-01 10:29             ` Mark Rutland
2018-06-01 10:42               ` Dave Martin
2018-05-14  9:46 ` [PATCH 07/18] arm64: remove sigreturn wrappers Mark Rutland
2018-05-14 11:07   ` Dave Martin
2018-05-14  9:46 ` [PATCH 08/18] arm64: convert raw syscall invocation to C Mark Rutland
2018-05-14 11:07   ` Dave Martin
2018-05-14 11:41     ` Mark Rutland
2018-05-14 12:53       ` Dave Martin
2018-05-14 20:24       ` Dominik Brodowski
2018-05-15  8:22         ` Mark Rutland
2018-05-15 10:01           ` Dominik Brodowski
2018-05-15 10:13             ` Mark Rutland
2018-05-14 18:00   ` Dominik Brodowski
2018-05-15  8:18     ` Mark Rutland
2018-05-14  9:46 ` [PATCH 09/18] arm64: convert syscall trace logic " Mark Rutland
2018-05-14  9:46 ` [PATCH 10/18] arm64: convert native/compat syscall entry " Mark Rutland
2018-05-14 11:07   ` Dave Martin
2018-05-14 11:58     ` Mark Rutland
2018-05-14 14:43       ` Dave Martin
2018-05-14 15:01         ` Mark Rutland
2018-05-14  9:46 ` [PATCH 11/18] arm64: zero GPRs upon entry from EL0 Mark Rutland
2018-05-14 11:07   ` Dave Martin
2018-05-14  9:46 ` [PATCH 12/18] kernel: add ksys_personality() Mark Rutland
2018-05-14 11:08   ` Dave Martin
2018-05-14 12:07   ` Christoph Hellwig
2018-05-15  9:56     ` Mark Rutland
2018-05-14  9:46 ` [PATCH 13/18] kernel: add kcompat_sys_{f,}statfs64() Mark Rutland
2018-05-14 17:14   ` Mark Rutland
2018-05-14 20:34     ` Dominik Brodowski
2018-05-15  9:53       ` Mark Rutland
2018-05-15  9:58         ` Dominik Brodowski
2018-05-14  9:46 ` [PATCH 14/18] arm64: remove in-kernel call to sys_personality() Mark Rutland
2018-05-14  9:46 ` [PATCH 15/18] arm64: use {COMPAT,}SYSCALL_DEFINE0 for sigreturn Mark Rutland
2018-05-14  9:46 ` [PATCH 16/18] arm64: use SYSCALL_DEFINE6() for mmap Mark Rutland
2018-05-14  9:46 ` [PATCH 17/18] arm64: convert compat wrappers to C Mark Rutland
2018-05-14 12:10   ` Christoph Hellwig
2018-05-14 12:43     ` Mark Rutland
2018-05-14  9:46 ` [PATCH 18/18] arm64: implement syscall wrappers Mark Rutland
2018-05-14 20:57   ` Dominik Brodowski
2018-05-15  8:37     ` Mark Rutland

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