From: catalin.marinas@arm•com (Catalin Marinas)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] Fix for the arm64 kern_addr_valid() function
Date: Tue, 29 Apr 2014 15:25:42 +0100 [thread overview]
Message-ID: <20140429142542.GI17007@arm.com> (raw)
In-Reply-To: <20140416075144.GA29754@arm.com>
On Wed, Apr 16, 2014 at 08:51:44AM +0100, Will Deacon wrote:
> On Tue, Apr 15, 2014 at 06:53:24PM +0100, Dave Anderson wrote:
> > Fix for the arm64 kern_addr_valid() function to recognize
> > virtual addresses in the kernel logical memory map. The
> > function fails as written because it does not check whether
> > the addresses in that region are mapped at the pmd level to
> > 2MB or 512MB pages, continues the page table walk to the
> > pte level, and issues a garbage value to pfn_valid().
> >
> > Tested on 4K-page and 64K-page kernels.
> >
> > Signed-off-by: Dave Anderson <anderson@redhat•com>
> > ---
> > arch/arm64/mm/mmu.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 6b7e895..0a472c4 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -374,6 +374,9 @@ int kern_addr_valid(unsigned long addr)
> > if (pmd_none(*pmd))
> > return 0;
> >
> > + if (pmd_sect(*pmd))
> > + return pfn_valid(pmd_pfn(*pmd));
> > +
> > pte = pte_offset_kernel(pmd, addr);
> > if (pte_none(*pte))
> > return 0;
>
> Whilst this patch looks fine to me, I wonder whether walking the page tables
> is really necessary for this function? The only user is fs/proc/kcore.c,
> which basically wants to know if a lowmem address is actually backed by
> physical memory. Our current implementation of kern_addr_valid will return
> true even for MMIO mappings,
There is still a pfn_valid() check, so MMIO mappings wouldn't return
true.
> whilst I think we could actually just do
> something like:
>
>
> if ((((long)addr) >> VA_BITS) != -1UL)
> return 0;
>
> return pfn_valid(__pa(addr) >> PAGE_SHIFT);
>
> Am I missing something here?
__pa(addr) isn't valid for vmalloc/ioremap addresses (which would pass
the VA_BITS test above).
I would go with Dave's original patch for now. We've discussing change
the memory map a bit for the kernel at some point in the future with
PHYS_OFFSET always 0 and the kernel text/data mapped at a different
address from PAGE_OFFSET (similar to x86_64). If we get there, this
function would work unmodified.
--
Catalin
next prev parent reply other threads:[~2014-04-29 14:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-15 17:53 [PATCH] Fix for the arm64 kern_addr_valid() function Dave Anderson
2014-04-16 7:51 ` Will Deacon
2014-04-16 13:35 ` Dave Anderson
2014-04-29 14:25 ` Catalin Marinas [this message]
2014-04-29 14:34 ` Don Dutile
2014-04-29 15:00 ` Will Deacon
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