All of lore.kernel.org
 help / color / mirror / Atom feed
From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>
Subject: [PATCH 2/2] x86/PoD: move increment of entry count
Date: Wed, 1 Dec 2021 12:02:02 +0100	[thread overview]
Message-ID: <d92ec1b7-6cde-7efc-2c6a-3dc3696b957f@suse.com> (raw)
In-Reply-To: <ac46f25b-e669-f309-b36e-c4760e10479e@suse.com>

When not holding the PoD lock across the entire region covering P2M
update and stats update, the entry count should indicate too large a
value in preference to a too small one, to avoid functions bailing early
when they find the count is zero. Hence increments should happen ahead
of P2M updates, while decrements should happen only after. Deal with the
one place where this hasn't been the case yet.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -1345,19 +1345,15 @@ mark_populate_on_demand(struct domain *d
         }
     }
 
+    pod_lock(p2m);
+    p2m->pod.entry_count += (1UL << order) - pod_count;
+    pod_unlock(p2m);
+
     /* Now, actually do the two-way mapping */
     rc = p2m_set_entry(p2m, gfn, INVALID_MFN, order,
                        p2m_populate_on_demand, p2m->default_access);
     if ( rc == 0 )
-    {
-        pod_lock(p2m);
-        p2m->pod.entry_count += 1UL << order;
-        p2m->pod.entry_count -= pod_count;
-        BUG_ON(p2m->pod.entry_count < 0);
-        pod_unlock(p2m);
-
         ioreq_request_mapcache_invalidate(d);
-    }
     else if ( order )
     {
         /*
@@ -1369,6 +1365,13 @@ mark_populate_on_demand(struct domain *d
                d, gfn_l, order, rc);
         domain_crash(d);
     }
+    else if ( !pod_count )
+    {
+        pod_lock(p2m);
+        BUG_ON(!p2m->pod.entry_count);
+        --p2m->pod.entry_count;
+        pod_unlock(p2m);
+    }
 
 out:
     gfn_unlock(p2m, gfn, order);
When not holding the PoD lock across the entire region covering P2M
update and stats update, the entry count should indicate too large a
value in preference to a too small one, to avoid functions bailing early
when they find the count is zero. Hence increments should happen ahead
of P2M updates, while decrements should happen only after. Deal with the
one place where this hasn't been the case yet.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -1345,19 +1345,15 @@ mark_populate_on_demand(struct domain *d
         }
     }
 
+    pod_lock(p2m);
+    p2m->pod.entry_count += (1UL << order) - pod_count;
+    pod_unlock(p2m);
+
     /* Now, actually do the two-way mapping */
     rc = p2m_set_entry(p2m, gfn, INVALID_MFN, order,
                        p2m_populate_on_demand, p2m->default_access);
     if ( rc == 0 )
-    {
-        pod_lock(p2m);
-        p2m->pod.entry_count += 1UL << order;
-        p2m->pod.entry_count -= pod_count;
-        BUG_ON(p2m->pod.entry_count < 0);
-        pod_unlock(p2m);
-
         ioreq_request_mapcache_invalidate(d);
-    }
     else if ( order )
     {
         /*
@@ -1369,6 +1365,13 @@ mark_populate_on_demand(struct domain *d
                d, gfn_l, order, rc);
         domain_crash(d);
     }
+    else if ( !pod_count )
+    {
+        pod_lock(p2m);
+        BUG_ON(!p2m->pod.entry_count);
+        --p2m->pod.entry_count;
+        pod_unlock(p2m);
+    }
 
 out:
     gfn_unlock(p2m, gfn, order);



  parent reply	other threads:[~2021-12-01 11:02 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-01 11:00 [PATCH 0/2] x86/mm: XSA-389 follow-up Jan Beulich
2021-12-01 11:01 ` [PATCH 1/2] x86/mm: don't open-code p2m_is_pod() Jan Beulich
2021-12-01 11:22   ` Andrew Cooper
2021-12-02 19:10   ` Tim Deegan
2021-12-01 11:02 ` Jan Beulich [this message]
2021-12-01 11:27   ` [PATCH 2/2] x86/PoD: move increment of entry count Andrew Cooper
2021-12-01 11:50     ` Jan Beulich
2021-12-01 11:52 ` Jan Beulich
2021-12-01 15:40   ` Andrew Cooper
2022-01-04 10:57 ` [PATCH v2] " Jan Beulich
2022-01-27 15:04   ` Ping: " Jan Beulich
2022-02-24 13:04     ` Ping²: " Jan Beulich
2024-03-11 16:04   ` George Dunlap
2024-03-12 13:17     ` Jan Beulich
2024-03-12 15:22 ` [PATCH v3] x86/PoD: tie together P2M update and " Jan Beulich
2024-03-13 10:58   ` George Dunlap
2024-03-13 12:19     ` Jan Beulich
2024-03-13 12:25       ` George Dunlap
2024-03-13 12:25         ` George Dunlap
2024-03-13 14:00 ` [PATCH v4] " Jan Beulich
2024-03-13 16:31   ` George Dunlap
2024-03-14  6:59     ` Jan Beulich
2024-03-19 13:22 ` [PATCH v5] " Jan Beulich
2024-03-20  9:50   ` George Dunlap

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=d92ec1b7-6cde-7efc-2c6a-3dc3696b957f@suse.com \
    --to=jbeulich@suse.com \
    --cc=andrew.cooper3@citrix.com \
    --cc=george.dunlap@citrix.com \
    --cc=roger.pau@citrix.com \
    --cc=wl@xen.org \
    --cc=xen-devel@lists.xenproject.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.