On Tue, Nov 20, 2018 at 02:59:32AM +0000, Williams, Dan J wrote:
> On Mon, 2018-11-19 at 15:43 -0800, Dave Hansen wrote:
> > On 11/19/18 3:19 PM, Dan Williams wrote:
> > > Andy wondered why a path that can sleep was using __flush_tlb_all()
> > > [1]
> > > and Dave confirmed the expectation for TLB flush is for modifying /
> > > invalidating existing pte entries, but not initial population [2].
> >
> > I _think_ this is OK.
> >
> > But, could we sprinkle a few WARN_ON_ONCE(p*_present()) calls in
> > there
> > to help us sleep at night?
>
> Well, I'm having nightmares now because my naive patch to sprinkle some
> WARN_ON_ONCE() calls is leading to my VM live locking at boot... no
> backtrace. If I revert the patch below and just go with the
> __flush_tlb_all() removal it seems fine.
>
> I'm going to set this aside for a bit, but if anyone has any thoughts
> in the meantime I'd appreciate it.
Have you tried using early_printk ?
So kernel_physical_mapping_init() has a comment that states the virtual
and physical addresses we create mappings for should be PMD aligned,
which implies pud/p4d could have overlap between the mappings.
But in that case, I would expect the new and old values to match.
So maybe you should be checking something like:
WARN_ON_ONCE(pud_present(*pud) && !pud_same(pud, new));
> @@ -573,6 +578,7 @@ phys_pud_init(pud_t *pud_page, unsigned long paddr, unsigned long paddr_end,
> E820_TYPE_RAM) &&
> !e820__mapped_any(paddr & PUD_MASK, paddr_next,
> E820_TYPE_RESERVED_KERN))
> + WARN_ON_ONCE(pud_present(*pud));
> set_pud(pud, __pud(0));
> continue;
> }
> @@ -610,6 +616,7 @@ phys_pud_init(pud_t *pud_page, unsigned long paddr, unsigned long paddr_end,
> if (page_size_mask & (1<<PG_LEVEL_1G)) {
> pages++;
> spin_lock(&init_mm.page_table_lock);
> + WARN_ON_ONCE(pud_present(*pud));
> set_pte((pte_t *)pud,
> pfn_pte((paddr & PUD_MASK) >> PAGE_SHIFT,
> PAGE_KERNEL_LARGE));
> @@ -623,6 +630,7 @@ phys_pud_init(pud_t *pud_page, unsigned long paddr, unsigned long paddr_end,
> page_size_mask, prot);
>
> spin_lock(&init_mm.page_table_lock);
> + WARN_ON_ONCE(pud_present(*pud));
> pud_populate(&init_mm, pud, pmd);
> spin_unlock(&init_mm.page_table_lock);
> }
> @@ -657,6 +665,7 @@ phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end,
> E820_TYPE_RAM) &&
> !e820__mapped_any(paddr & P4D_MASK, paddr_next,
> E820_TYPE_RESERVED_KERN))
> + WARN_ON_ONCE(p4d_present(*p4d));
> set_p4d(p4d, __p4d(0));
> continue;
> }
> @@ -674,6 +683,7 @@ phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end,
> page_size_mask);
>
> spin_lock(&init_mm.page_table_lock);
> + WARN_ON_ONCE(p4d_present(*p4d));
> p4d_populate(&init_mm, p4d, pud);
> spin_unlock(&init_mm.page_table_lock);
> }
