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From: Toshi Kani <toshi.kani@hp.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: akpm@linux-foundation.org, hpa@zytor.com, tglx@linutronix.de,
	mingo@redhat.com, arnd@arndb.de, linux-mm@kvack.org,
	x86@kernel.org, linux-kernel@vger.kernel.org, Elliott@hp.com
Subject: Re: [PATCH v2 5/7] x86, mm: Support huge KVA mappings on x86
Date: Tue, 10 Feb 2015 15:13:17 -0700	[thread overview]
Message-ID: <1423606397.1128.20.camel@misato.fc.hp.com> (raw)
In-Reply-To: <54DA6F38.4050902@intel.com>

On Tue, 2015-02-10 at 12:51 -0800, Dave Hansen wrote:
> On 02/10/2015 12:42 PM, Toshi Kani wrote:
> > On Tue, 2015-02-10 at 10:59 -0800, Dave Hansen wrote:
> >> On 02/09/2015 02:45 PM, Toshi Kani wrote:
> >>> Implement huge KVA mapping interfaces on x86.  Select
> >>> HAVE_ARCH_HUGE_VMAP when X86_64 or X86_32 with X86_PAE is set.
> >>> Without X86_PAE set, the X86_32 kernel has the 2-level page
> >>> tables and cannot provide the huge KVA mappings.
> >>
> >> Not that it's a big deal, but what's the limitation with the 2-level
> >> page tables on 32-bit?  We have a 4MB large page size available there
> >> and we already use it for the kernel linear mapping.
> > 
> > ioremap() calls arch-neutral ioremap_page_range() to set up I/O mappings
> > with PTEs.  This patch-set enables ioremap_page_range() to set up PUD &
> > PMD mappings.  With 2-level page table, I do not think this PUD/PMD
> > mapping code works unless we add some special code.
> 
> What actually breaks, though?
> 
> Can't you just disable the pud code via ioremap_pud_enabled()?

That's what v1 did, and I found in testing that the PMD mapping code did
not work when PAE was unset.  I think we need special handling similar
to one_md_table_init(), which returns pgd as pmd in case of non-PAE.
ioremap_page_range() does not have such handling and I thought it would
be worth adding it.

Thanks,
-Toshi



WARNING: multiple messages have this Message-ID (diff)
From: Toshi Kani <toshi.kani@hp.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: akpm@linux-foundation.org, hpa@zytor.com, tglx@linutronix.de,
	mingo@redhat.com, arnd@arndb.de, linux-mm@kvack.org,
	x86@kernel.org, linux-kernel@vger.kernel.org, Elliott@hp.com
Subject: Re: [PATCH v2 5/7] x86, mm: Support huge KVA mappings on x86
Date: Tue, 10 Feb 2015 15:13:17 -0700	[thread overview]
Message-ID: <1423606397.1128.20.camel@misato.fc.hp.com> (raw)
In-Reply-To: <54DA6F38.4050902@intel.com>

On Tue, 2015-02-10 at 12:51 -0800, Dave Hansen wrote:
> On 02/10/2015 12:42 PM, Toshi Kani wrote:
> > On Tue, 2015-02-10 at 10:59 -0800, Dave Hansen wrote:
> >> On 02/09/2015 02:45 PM, Toshi Kani wrote:
> >>> Implement huge KVA mapping interfaces on x86.  Select
> >>> HAVE_ARCH_HUGE_VMAP when X86_64 or X86_32 with X86_PAE is set.
> >>> Without X86_PAE set, the X86_32 kernel has the 2-level page
> >>> tables and cannot provide the huge KVA mappings.
> >>
> >> Not that it's a big deal, but what's the limitation with the 2-level
> >> page tables on 32-bit?  We have a 4MB large page size available there
> >> and we already use it for the kernel linear mapping.
> > 
> > ioremap() calls arch-neutral ioremap_page_range() to set up I/O mappings
> > with PTEs.  This patch-set enables ioremap_page_range() to set up PUD &
> > PMD mappings.  With 2-level page table, I do not think this PUD/PMD
> > mapping code works unless we add some special code.
> 
> What actually breaks, though?
> 
> Can't you just disable the pud code via ioremap_pud_enabled()?

That's what v1 did, and I found in testing that the PMD mapping code did
not work when PAE was unset.  I think we need special handling similar
to one_md_table_init(), which returns pgd as pmd in case of non-PAE.
ioremap_page_range() does not have such handling and I thought it would
be worth adding it.

Thanks,
-Toshi


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  reply	other threads:[~2015-02-10 22:13 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-09 22:45 [PATCH v2 0/7] Kernel huge I/O mapping support Toshi Kani
2015-02-09 22:45 ` Toshi Kani
2015-02-09 22:45 ` [PATCH v2 1/7] mm: Change __get_vm_area_node() to use fls_long() Toshi Kani
2015-02-09 22:45   ` Toshi Kani
2015-02-09 22:45 ` [PATCH v2 2/7] lib: Add huge I/O map capability interfaces Toshi Kani
2015-02-09 22:45   ` Toshi Kani
2015-02-09 22:45 ` [PATCH v2 3/7] mm: Change ioremap to set up huge I/O mappings Toshi Kani
2015-02-09 22:45   ` Toshi Kani
2015-02-09 22:45 ` [PATCH v2 4/7] mm: Change vunmap to tear down huge KVA mappings Toshi Kani
2015-02-09 22:45   ` Toshi Kani
2015-02-09 22:45 ` [PATCH v2 5/7] x86, mm: Support huge KVA mappings on x86 Toshi Kani
2015-02-09 22:45   ` Toshi Kani
2015-02-10 18:59   ` Dave Hansen
2015-02-10 18:59     ` Dave Hansen
2015-02-10 20:42     ` Toshi Kani
2015-02-10 20:42       ` Toshi Kani
2015-02-10 20:51       ` Dave Hansen
2015-02-10 20:51         ` Dave Hansen
2015-02-10 22:13         ` Toshi Kani [this message]
2015-02-10 22:13           ` Toshi Kani
2015-02-10 22:20           ` Toshi Kani
2015-02-10 22:20             ` Toshi Kani
2015-02-10 23:10           ` Toshi Kani
2015-02-10 23:10             ` Toshi Kani
2015-03-03  0:37             ` Toshi Kani
2015-03-03  0:37               ` Toshi Kani
2015-02-09 22:45 ` [PATCH v2 6/7] x86, mm: Support huge I/O " Toshi Kani
2015-02-09 22:45   ` Toshi Kani
2015-02-18 20:44   ` Ingo Molnar
2015-02-18 20:44     ` Ingo Molnar
2015-02-18 21:13     ` Toshi Kani
2015-02-18 21:13       ` Toshi Kani
2015-02-18 21:15       ` Ingo Molnar
2015-02-18 21:15         ` Ingo Molnar
2015-02-18 21:33         ` Toshi Kani
2015-02-18 21:33           ` Toshi Kani
2015-02-18 21:57           ` Ingo Molnar
2015-02-18 21:57             ` Ingo Molnar
2015-02-18 22:14             ` Toshi Kani
2015-02-18 22:14               ` Toshi Kani
2015-02-09 22:45 ` [PATCH v2 7/7] mm: Add config HUGE_IOMAP to enable huge I/O mappings Toshi Kani
2015-02-09 22:45   ` Toshi Kani
2015-02-23 20:22 ` [PATCH v2 0/7] Kernel huge I/O mapping support Andrew Morton
2015-02-23 20:22   ` Andrew Morton
2015-02-23 23:54   ` Toshi Kani
2015-02-23 23:54     ` Toshi Kani
2015-02-24  8:09   ` Ingo Molnar
2015-02-24  8:09     ` Ingo Molnar
2015-03-02 15:51     ` Toshi Kani
2015-03-02 15:51       ` Toshi Kani

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