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Re: [RFC PATCH] x86/p2m-pt: do type recalculations with p2m read lock
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 3 Apr 2023 14:39:08 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 03 Apr 2023 12:39:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03.04.2023 12:14, Roger Pau Monne wrote:
> --- a/xen/arch/x86/mm/p2m-pt.c
> +++ b/xen/arch/x86/mm/p2m-pt.c
> @@ -486,9 +486,6 @@ static int cf_check do_recalc(struct p2m_domain *p2m,
> unsigned long gfn)
> p2m_type_t ot, nt;
> unsigned long mask = ~0UL << (level * PAGETABLE_ORDER);
>
> - if ( !valid_recalc(l1, e) )
> - P2M_DEBUG("bogus recalc leaf at d%d:%lx:%u\n",
> - p2m->domain->domain_id, gfn, level);
> ot = p2m_flags_to_type(l1e_get_flags(e));
> nt = p2m_recalc_type_range(true, ot, p2m, gfn & mask, gfn | ~mask);
> if ( nt != ot )
I'm afraid I neither understand why you make this change, nor why you
then leave the other use of valid_recalc() in place.
> @@ -538,9 +535,9 @@ int p2m_pt_handle_deferred_changes(uint64_t gpa)
> */
> ASSERT(!altp2m_active(current->domain));
>
> - p2m_lock(p2m);
> + p2m_read_lock(p2m);
> rc = do_recalc(p2m, PFN_DOWN(gpa));
> - p2m_unlock(p2m);
> + p2m_read_unlock(p2m);
>
> return rc;
> }
How can this be safe, when do_recalc() involves p2m_next_level(), which
may install new (intermediate) page tables?
Jan
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