From: catalin.marinas@arm.com (Catalin Marinas)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 14/14] ARM: elf: add new hwcap for identifying atomic ldrd/strd instructions
Date: Thu, 23 May 2013 09:50:07 +0100 [thread overview]
Message-ID: <20130523085006.GA16722@arm.com> (raw)
In-Reply-To: <20130522180942.GK16361@mudshark.cambridge.arm.com>
On Wed, May 22, 2013 at 07:09:42PM +0100, Will Deacon wrote:
> On Wed, May 22, 2013 at 09:47:44AM +0100, Catalin Marinas wrote:
> > On Tue, May 21, 2013 at 07:48:35PM +0100, Rob Herring wrote:
> > > On Mon, May 20, 2013 at 9:18 AM, Catalin Marinas
> > > <catalin.marinas@arm.com> wrote:
> > > > On Fri, May 17, 2013 at 06:07:53PM +0100, Will Deacon wrote:
> > > >> CPUs implementing LPAE have atomic ldrd/strd instructions, meaning that
> > > >> userspace software can avoid having to use the exclusive variants of
> > > >> these instructions if they wish.
> > > >>
> > > >> This patch advertises the atomicity of these instructions via the
> > > >> hwcaps, so userspace can detect this CPU feature.
> > > >>
> > > >> Reported-by: Vladimir Danushevsky <vladimir.danushevsky@oracle.com>
> > > >> Signed-off-by: Will Deacon <will.deacon@arm.com>
> > > > ...
> > > >> +
> > > >> + /* LPAE implies atomic ldrd/strd instructions */
> > > >> + vmsa = (read_cpuid_ext(CPUID_EXT_MMFR0) & 0xf) >> 0;
> > > >> + if (vmsa >= 5)
> > > >> + elf_hwcap |= HWCAP_LPAE;
> > > >
> > > > As I mentioned in the past, I don't agree with exposing the "LPAE"
> > > > feature to user-space, it's not a feature that user space should care
> > > > about. An atomic double hwcap is better and you can even make this per
> > > > CPU via __v7_proc.
> > >
> > > How does userspace know whether to install a non-LPAE or LPAE kernel
> > > in a generic way?
> >
> > This is a valid reason to expose LPAE to user, though elf_hwcap sounds a
> > bit strange.
>
> In lieu of anything else, do you mind if I continue with the patch as it
> stands?
OK, I give up ;)
--
Catalin
next prev parent reply other threads:[~2013-05-23 8:50 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-17 17:07 [PATCH 00/14] Random LPAE-related patches Will Deacon
2013-05-17 17:07 ` [PATCH 01/14] ARM: LPAE: use signed arithmetic for mask definitions Will Deacon
2013-05-17 17:07 ` [PATCH 02/14] ARM: LPAE: use phys_addr_t in alloc_init_pud() Will Deacon
2013-05-17 17:07 ` [PATCH 03/14] ARM: LPAE: use phys_addr_t in free_memmap() Will Deacon
2013-05-17 17:07 ` [PATCH 04/14] ARM: LPAE: use phys_addr_t for initrd location Will Deacon
2013-05-17 17:07 ` [PATCH 05/14] ARM: LPAE: use phys_addr_t in switch_mm() Will Deacon
2013-05-17 17:07 ` [PATCH 06/14] ARM: LPAE: use 64-bit accessors for TTBR registers Will Deacon
2013-05-17 17:07 ` [PATCH 07/14] ARM: LPAE: factor out T1SZ and TTBR1 computations Will Deacon
2013-05-17 17:07 ` [PATCH 08/14] ARM: LPAE: accomodate >32-bit addresses for page table base Will Deacon
2013-05-17 17:07 ` [PATCH 09/14] ARM: mm: use physical addresses in highmem sanity checks Will Deacon
2013-05-17 17:07 ` [PATCH 10/14] ARM: fix type of PHYS_PFN_OFFSET to unsigned long Will Deacon
2013-05-17 17:07 ` [PATCH 11/14] ARM: mm: cleanup checks for membank overlap with vmalloc area Will Deacon
2013-05-17 17:07 ` [PATCH 12/14] ARM: mm: clean up membank size limit checks Will Deacon
2013-05-17 17:07 ` [PATCH 13/14] ARM: lpae: fix definition of PTE_HWTABLE_PTRS Will Deacon
2013-05-17 17:07 ` [PATCH 14/14] ARM: elf: add new hwcap for identifying atomic ldrd/strd instructions Will Deacon
2013-05-20 14:18 ` Catalin Marinas
2013-05-20 14:24 ` Will Deacon
2013-05-20 15:11 ` Catalin Marinas
2013-05-20 16:04 ` Will Deacon
2013-05-20 17:13 ` Catalin Marinas
2013-05-21 18:02 ` Will Deacon
2013-05-22 8:43 ` Catalin Marinas
2013-05-21 18:48 ` Rob Herring
2013-05-22 8:47 ` Catalin Marinas
2013-05-22 18:09 ` Will Deacon
2013-05-23 8:50 ` Catalin Marinas [this message]
2013-05-17 18:23 ` [PATCH 00/14] Random LPAE-related patches Santosh Shilimkar
2013-05-30 13:31 ` Subash Patel
2013-05-30 15:03 ` Will Deacon
2013-05-31 0:38 ` Kukjin Kim
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