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.
---
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index de95db8ac52f..ecdf917def4c 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -432,6 +432,7 @@ phys_pte_init(pte_t *pte_page, unsigned long paddr,
unsigned long paddr_end,
E820_TYPE_RAM) &&
!e820__mapped_any(paddr & PAGE_MASK, paddr_next,
E820_TYPE_RESERVED_KERN))
+ WARN_ON_ONCE(pte_present(*pte));
set_pte(pte, __pte(0));
continue;
}
@@ -452,6 +453,7 @@ phys_pte_init(pte_t *pte_page, unsigned long paddr,
unsigned long paddr_end,
pr_info(" pte=%p addr=%lx pte=%016lx\n", pte, paddr,
pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL).pte);
pages++;
+ WARN_ON_ONCE(pte_present(*pte));
set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
paddr_last = (paddr & PAGE_MASK) + PAGE_SIZE;
}
@@ -487,6 +489,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long paddr,
unsigned long paddr_end,
E820_TYPE_RAM) &&
!e820__mapped_any(paddr & PMD_MASK, paddr_next,
E820_TYPE_RESERVED_KERN))
+ WARN_ON_ONCE(pmd_present(*pmd));
set_pmd(pmd, __pmd(0));
continue;
}
@@ -524,6 +527,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long paddr,
unsigned long paddr_end,
if (page_size_mask & (1<<PG_LEVEL_2M)) {
pages++;
spin_lock(&init_mm.page_table_lock);
+ WARN_ON_ONCE(pmd_present(*pmd));
set_pte((pte_t *)pmd,
pfn_pte((paddr & PMD_MASK) >> PAGE_SHIFT,
__pgprot(pgprot_val(prot) |
_PAGE_PSE)));
@@ -536,6 +540,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long paddr,
unsigned long paddr_end,
paddr_last = phys_pte_init(pte, paddr, paddr_end, new_prot);
spin_lock(&init_mm.page_table_lock);
+ WARN_ON_ONCE(pmd_present(*pmd));
pmd_populate_kernel(&init_mm, pmd, pte);
spin_unlock(&init_mm.page_table_lock);
}
@@ -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);
}
