Messages in this thread | | | Date | Thu, 11 Jun 2015 16:04:04 -0400 | From | Boris Ostrovsky <> | Subject | Re: [PATCH 06/12] x86/mm: Enable and use the arch_pgd_init_late() method |
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On 06/11/2015 10:07 AM, Ingo Molnar wrote:
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c > index fb0a9dd1d6e4..e0bf90470d70 100644 > --- a/arch/x86/mm/pgtable.c > +++ b/arch/x86/mm/pgtable.c > @@ -391,6 +391,63 @@ pgd_t *pgd_alloc(struct mm_struct *mm) > return NULL; > } > > +/* > + * Initialize the kernel portion of the PGD. > + * > + * This is done separately, because pgd_alloc() happens when > + * the task is not on the task list yet - and PGD updates > + * happen by walking the task list. > + * > + * No locking is needed here, as we just copy over the reference > + * PGD. The reference PGD (pgtable_init) is only ever expanded > + * at the highest, PGD level. Thus any other task extending it > + * will first update the reference PGD, then modify the task PGDs. > + */ > +void arch_pgd_init_late(struct mm_struct *mm, pgd_t *pgd) > +{ > + /* > + * This is called after a new MM has been made visible > + * in fork() or exec(). > + * > + * This barrier makes sure the MM is visible to new RCU > + * walkers before we initialize it, so that we don't miss > + * updates: > + */ > + smp_wmb(); > + > + /* > + * If the pgd points to a shared pagetable level (either the > + * ptes in non-PAE, or shared PMD in PAE), then just copy the > + * references from swapper_pg_dir: > + */ > + if (CONFIG_PGTABLE_LEVELS == 2 || > + (CONFIG_PGTABLE_LEVELS == 3 && SHARED_KERNEL_PMD) || > + CONFIG_PGTABLE_LEVELS == 4) { > + > + pgd_t *pgd_src = swapper_pg_dir + KERNEL_PGD_BOUNDARY; > + pgd_t *pgd_dst = pgd + KERNEL_PGD_BOUNDARY; > + int i; > + > + for (i = 0; i < KERNEL_PGD_PTRS; i++, pgd_src++, pgd_dst++) { > + /* > + * This is lock-less, so it can race with PGD updates > + * coming from vmalloc() or CPA methods, but it's safe, > + * because: > + * > + * 1) this PGD is not in use yet, we have still not > + * scheduled this task. > + * 2) we only ever extend PGD entries > + * > + * So if we observe a non-zero PGD entry we can copy it, > + * it won't change from under us. Parallel updates (new > + * allocations) will modify our (already visible) PGD: > + */ > + if (pgd_val(*pgd_src)) > + WRITE_ONCE(*pgd_dst, *pgd_src);
This should be set_pgd(pgd_dst, *pgd_src) in order for it to work as a Xen PV guest.
I don't know whether anything would need to be done wrt WRITE_ONCE. Perhaps put it into native_set_pgd()?
-boris
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