From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <george.dunlap@citrix.com>
Subject: [PATCH] x86/PoD: defer nested P2M flushes
Date: Mon, 11 Oct 2021 10:17:08 +0200 [thread overview]
Message-ID: <e47d51c6-1b4b-2f72-6e12-070df66c30e2@suse.com> (raw)
With NPT or shadow in use, the p2m_set_entry() -> p2m_pt_set_entry() ->
write_p2m_entry() -> p2m_flush_nestedp2m() call sequence triggers a lock
order violation when the PoD lock is held around it. Hence such flushing
needs to be deferred. Steal the approach from p2m_change_type_range().
Similarly for EPT I think ept_set_entry() -> ept_sync_domain() ->
ept_sync_domain_prepare() -> p2m_flush_nestedp2m() is affected.
Reported-by: Elliott Mitchell <ehem+xen@m5p.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -24,6 +24,7 @@
#include <xen/mm.h>
#include <xen/sched.h>
#include <xen/trace.h>
+#include <asm/hvm/nestedhvm.h>
#include <asm/page.h>
#include <asm/paging.h>
#include <asm/p2m.h>
@@ -494,6 +495,13 @@ p2m_pod_offline_or_broken_replace(struct
static int
p2m_pod_zero_check_superpage(struct p2m_domain *p2m, gfn_t gfn);
+static void pod_unlock_and_flush(struct p2m_domain *p2m)
+{
+ pod_unlock(p2m);
+ p2m->defer_nested_flush = false;
+ if ( nestedhvm_enabled(p2m->domain) )
+ p2m_flush_nestedp2m(p2m->domain);
+}
/*
* This function is needed for two reasons:
@@ -514,6 +522,7 @@ p2m_pod_decrease_reservation(struct doma
gfn_lock(p2m, gfn, order);
pod_lock(p2m);
+ p2m->defer_nested_flush = true;
/*
* If we don't have any outstanding PoD entries, let things take their
@@ -665,7 +674,7 @@ out_entry_check:
}
out_unlock:
- pod_unlock(p2m);
+ pod_unlock_and_flush(p2m);
gfn_unlock(p2m, gfn, order);
return ret;
}
@@ -1144,8 +1153,10 @@ p2m_pod_demand_populate(struct p2m_domai
* won't start until we're done.
*/
if ( unlikely(d->is_dying) )
- goto out_fail;
-
+ {
+ pod_unlock(p2m);
+ return false;
+ }
/*
* Because PoD does not have cache list for 1GB pages, it has to remap
@@ -1167,6 +1178,8 @@ p2m_pod_demand_populate(struct p2m_domai
p2m_populate_on_demand, p2m->default_access);
}
+ p2m->defer_nested_flush = true;
+
/* Only reclaim if we're in actual need of more cache. */
if ( p2m->pod.entry_count > p2m->pod.count )
pod_eager_reclaim(p2m);
@@ -1229,8 +1242,9 @@ p2m_pod_demand_populate(struct p2m_domai
__trace_var(TRC_MEM_POD_POPULATE, 0, sizeof(t), &t);
}
- pod_unlock(p2m);
+ pod_unlock_and_flush(p2m);
return true;
+
out_of_memory:
pod_unlock(p2m);
@@ -1239,12 +1253,14 @@ out_of_memory:
p2m->pod.entry_count, current->domain->domain_id);
domain_crash(d);
return false;
+
out_fail:
- pod_unlock(p2m);
+ pod_unlock_and_flush(p2m);
return false;
+
remap_and_retry:
BUG_ON(order != PAGE_ORDER_2M);
- pod_unlock(p2m);
+ pod_unlock_and_flush(p2m);
/*
* Remap this 2-meg region in singleton chunks. See the comment on the
next reply other threads:[~2021-10-11 8:17 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-11 8:17 Jan Beulich [this message]
2021-10-18 8:34 ` Ping: [PATCH] x86/PoD: defer nested P2M flushes Jan Beulich
2021-10-19 8:09 ` Roger Pau Monné
2021-10-19 8:17 ` Jan Beulich
2021-10-19 8:19 ` Jan Beulich
2021-10-19 10:39 ` Roger Pau Monné
2021-10-19 10:50 ` Jan Beulich
2021-10-19 10:41 ` Roger Pau Monné
2021-10-19 11:58 ` Jan Beulich
2021-10-19 12:59 ` Roger Pau Monné
2021-10-19 13:14 ` Jan Beulich
2021-10-19 13:36 ` Roger Pau Monné
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