On 02/27/2020 09:33 AM, Andrew Morton wrote: > On Thu, 27 Feb 2020 08:04:05 +0530 Anshuman Khandual <anshuman.khandual@xxxxxxx> 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.morse@xxxxxxx> >> >> 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?? My patch just missed your response here within a minute :) Please consider this. It has been tested on x86 and arm64. https://patchwork.kernel.org/patch/11407715/ > > > > From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > 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 <cai@xxxxxx> > Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> > Cc: James Morse <james.morse@xxxxxxx> > Cc: Christophe Leroy <christophe.leroy@xxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > 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; > _ > >
