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?? 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; _
