On Thu, 27 Feb 2020 08:04:05 +0530 Anshuman Khandual
<anshuman.khand...@arm.com> wrote:
> > Must be something wrong with the following in debug_vm_pgtable()
> >
> > paddr = __pa(&start_kernel);
> >
> > Is there any explaination why start_kernel() is not in linear memory on
> > ARM64 ?
>
>
> Cc: + James Morse <james.mo...@arm.com>
>
> This warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
> i.e 'start_kernel' which might be outside the linear map. This happens due to
> kernel mapping position randomization with KASLR. Adding James here in case he
> might like to add more.
>
> __pa_symbol() should have been used instead, for accessing the physical
> address
> here. On arm64 __pa() does check for linear address with __is_lm_address() and
> switch accordingly if it is a kernel text symbol. Nevertheless, its much
> better
> to use __pa_symbol() here rather than __pa().
>
> Rather than respining the patch once more, will just send a fix replacing this
> helper __pa() with __pa_symbol() for Andrew to pick up as this patch is
> already
> part of linux-next (next-20200226). But can definitely respin if that will be
> preferred.
I didn't see this fix? I assume it's this? If so, are we sure it's OK to be
added to -next without testing??
From: Andrew Morton <a...@linux-foundation.org>
Subject: mm-debug-add-tests-validating-architecture-page-table-helpers-fix
A warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
i.e 'start_kernel' which might be outside the linear map. This happens
due to kernel mapping position randomization with KASLR.
__pa_symbol() should have been used instead, for accessing the physical
address here. On arm64 __pa() does check for linear address with
__is_lm_address() and switch accordingly if it is a kernel text symbol.
Nevertheless, its much better to use __pa_symbol() here rather than
__pa().
Reported-by: Qian Cai <c...@lca.pw>
Cc: Anshuman Khandual <anshuman.khand...@arm.com>
Cc: James Morse <james.mo...@arm.com>
Cc: Christophe Leroy <christophe.le...@c-s.fr>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
---
mm/debug_vm_pgtable.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
---
a/mm/debug_vm_pgtable.c~mm-debug-add-tests-validating-architecture-page-table-helpers-fix
+++ a/mm/debug_vm_pgtable.c
@@ -331,7 +331,7 @@ void __init debug_vm_pgtable(void)
* helps avoid large memory block allocations to be used for mapping
* at higher page table levels.
*/
- paddr = __pa(&start_kernel);
+ paddr = __pa_symbol(&start_kernel);
pte_aligned = (paddr & PAGE_MASK) >> PAGE_SHIFT;
pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
_
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