diff mbox

[v2,1/2] arm64: vmemmap: use virtual projection of linear region

Message ID 20160309113214.GB1535@rric.localdomain (mailing list archive)
State New, archived
Headers show

Commit Message

Robert Richter March 9, 2016, 11:32 a.m. UTC 
On 08.03.16 17:31:05, Ard Biesheuvel wrote:
> On 8 March 2016 at 09:15, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> >
> >
> >> On 8 mrt. 2016, at 08:07, David Daney <ddaney.cavm@gmail.com> wrote:
> >>
> >>> On 02/26/2016 08:57 AM, Ard Biesheuvel wrote:
> >>> Commit dd006da21646 ("arm64: mm: increase VA range of identity map") made
> >>> some changes to the memory mapping code to allow physical memory to reside
> >>> at an offset that exceeds the size of the virtual mapping.
> >>>
> >>> However, since the size of the vmemmap area is proportional to the size of
> >>> the VA area, but it is populated relative to the physical space, we may
> >>> end up with the struct page array being mapped outside of the vmemmap
> >>> region. For instance, on my Seattle A0 box, I can see the following output
> >>> in the dmesg log.
> >>>
> >>>    vmemmap : 0xffffffbdc0000000 - 0xffffffbfc0000000   (     8 GB maximum)
> >>>              0xffffffbfc0000000 - 0xffffffbfd0000000   (   256 MB actual)
> >>>
> >>> We can fix this by deciding that the vmemmap region is not a projection of
> >>> the physical space, but of the virtual space above PAGE_OFFSET, i.e., the
> >>> linear region. This way, we are guaranteed that the vmemmap region is of
> >>> sufficient size, and we can even reduce the size by half.
> >>>
> >>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >>
> >> I see this commit now in Linus' kernel.org tree in v4.5-rc7.
> >>
> >> FYI:  I am seeing a crash that goes away when I revert this.  My kernel has some other modifications (our NUMA patches) so I haven't yet fully tracked this down on an unmodified kernel, but this is what I am getting:
> >>
> >
> 
> I managed to reproduce and diagnose this. The problem is that vmemmap
> is no longer zone aligned, which causes trouble in the zone based
> rounding that occurs in memory_present. The below patch fixes this by
> rounding down the subtracted offset. Since this implies that the
> region could stick off the other end, it also reverts the halving of
> the region size.

I have seen the same panic. The fix solves the problem. See enclosed

Comments

Robert Richter March 9, 2016, 11:36 a.m. UTC | #1 
On 09.03.16 12:32:14, Robert Richter wrote:
> On 08.03.16 17:31:05, Ard Biesheuvel wrote:
> > On 8 March 2016 at 09:15, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> > I managed to reproduce and diagnose this. The problem is that vmemmap
> > is no longer zone aligned, which causes trouble in the zone based
> > rounding that occurs in memory_present. The below patch fixes this by
> > rounding down the subtracted offset. Since this implies that the
> > region could stick off the other end, it also reverts the halving of
> > the region size.
> 
> I have seen the same panic. The fix solves the problem. See enclosed
> diff for reference as there was some patch corruption of the original.

So this is:

Tested-by: Robert Richter <rrichter@cavium.com>

-Robert
diff mbox

Patch

diff for reference as there was some patch corruption of the original.

Thanks,

-Robert


From 562760cc30905748cb851cc9aee2bb9d88c67d47 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Tue, 8 Mar 2016 17:31:05 +0700
Subject: [PATCH] arm64: vmemmap: Fix use virtual projection of linear region

Signed-off-by: Robert Richter <rrichter@cavium.com>
---
 arch/arm64/include/asm/pgtable.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index d9de87354869..98697488650f 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -40,7 +40,7 @@ 
  * VMALLOC_END: extends to the available space below vmmemmap, PCI I/O space,
  *	fixed mappings and modules
  */
-#define VMEMMAP_SIZE		ALIGN((1UL << (VA_BITS - PAGE_SHIFT - 1)) * sizeof(struct page), PUD_SIZE)
+#define VMEMMAP_SIZE		ALIGN((1UL << (VA_BITS - PAGE_SHIFT)) * sizeof(struct page), PUD_SIZE)
 
 #ifndef CONFIG_KASAN
 #define VMALLOC_START		(VA_START)
@@ -52,7 +52,7 @@ 
 #define VMALLOC_END		(PAGE_OFFSET - PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
 
 #define VMEMMAP_START		(VMALLOC_END + SZ_64K)
-#define vmemmap			((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
+#define vmemmap			((struct page *)VMEMMAP_START - ((memstart_addr >> PAGE_SHIFT) & PAGE_SECTION_MASK))
 
 #define FIRST_USER_ADDRESS	0UL