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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>,
	"Tim Deegan" <tim@xen.org>
Subject: [PATCH v4 3/3] x86/shadow: streamline shadow_get_page_from_l1e()
Date: Fri, 23 Apr 2021 12:54:04 +0200	[thread overview]
Message-ID: <a73a6dd7-0cca-9ffe-e27e-39671c16e74c@suse.com> (raw)
In-Reply-To: <3e7ad009-f062-d58a-9380-103ce1573a73@suse.com>

Trying get_page_from_l1e() up to three times isn't helpful; in debug
builds it may lead to log messages making things look as if there was a
problem somewhere. And there's no need to have more than one try: The
function can only possibly succeed for one domain passed as 3rd
argument (unless the page is an MMIO one to which both have access,
but MMIO pages should be "got" by specifying the requesting domain
anyway). Re-arrange things so just the one call gets made which has a
chance of succeeding.

The code could in principle be arranged such that there's only a single
call to get_page_from_l1e(), but the conditional would become pretty
complex then and hence hard to follow / understand / adjust.

The redundant (with shadow_mode_refcounts()) shadow_mode_translate()
gets dropped.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>
---
v5: Integrate into series. Re-base.

--- a/xen/arch/x86/mm/shadow/set.c
+++ b/xen/arch/x86/mm/shadow/set.c
@@ -109,40 +109,36 @@ shadow_get_page_from_l1e(shadow_l1e_t sl
     if ( pg && page_refcounting_suppressed(pg) )
         return 0;
 
-    res = get_page_from_l1e(sl1e, d, d);
+    if ( owner == dom_io )
+        owner = NULL;
 
     /*
      * If a privileged domain is attempting to install a map of a page it does
      * not own, we let it succeed anyway.
      */
-    if ( unlikely(res < 0) &&
-         !shadow_mode_translate(d) &&
-         owner && (d != owner) )
+    if ( owner && (d != owner) &&
+         !(res = xsm_priv_mapping(XSM_TARGET, d, owner)) )
     {
-        res = xsm_priv_mapping(XSM_TARGET, d, owner);
-        if ( !res )
-        {
-            res = get_page_from_l1e(sl1e, d, owner);
-            SHADOW_PRINTK("privileged %pd installs map of mfn %"PRI_mfn" owned by %pd: %s\n",
-                           d, mfn_x(mfn), owner,
-                           res >= 0 ? "success" : "failed");
-        }
+        res = get_page_from_l1e(sl1e, d, owner);
+        SHADOW_PRINTK("privileged %pd installs map of %pd's mfn %"PRI_mfn": %s\n",
+                      d, owner, mfn_x(mfn),
+                      res >= 0 ? "success" : "failed");
     }
-
     /* Okay, it might still be a grant mapping PTE.  Try it. */
-    if ( unlikely(res < 0) &&
-         (type == p2m_grant_map_rw ||
-          (type == p2m_grant_map_ro &&
-           !(shadow_l1e_get_flags(sl1e) & _PAGE_RW))) )
+    else if ( owner &&
+              (type == p2m_grant_map_rw ||
+               (type == p2m_grant_map_ro &&
+                !(shadow_l1e_get_flags(sl1e) & _PAGE_RW))) )
     {
         /*
          * It's a grant mapping.  The grant table implementation will
          * already have checked that we're supposed to have access, so
          * we can just grab a reference directly.
          */
-        if ( owner )
-            res = get_page_from_l1e(sl1e, d, owner);
+        res = get_page_from_l1e(sl1e, d, owner);
     }
+    else
+        res = get_page_from_l1e(sl1e, d, d);
 
     if ( unlikely(res < 0) )
     {



  parent reply	other threads:[~2021-04-23 10:54 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-22 10:55 [PATCH v3 0/2] VMX: apic access page handling adjustments Jan Beulich
2021-02-22 10:56 ` [PATCH v3 1/2][4.15] VMX: delay p2m insertion of APIC access page Jan Beulich
2021-02-22 11:25   ` Ian Jackson
2021-02-22 14:05     ` Jan Beulich
2021-02-22 17:17       ` Ian Jackson
2021-02-22 12:15   ` Roger Pau Monné
2021-02-25  8:44   ` Jan Beulich
2021-02-26  7:06     ` Tian, Kevin
2021-02-22 10:57 ` [PATCH v3 2/2] VMX: use a single, global " Jan Beulich
2021-03-01  2:34   ` Tian, Kevin
2021-03-01  8:18     ` Jan Beulich
2021-04-12 10:40 ` [PATCH v4] " Jan Beulich
2021-04-12 15:31   ` Roger Pau Monné
2021-04-13  9:24     ` Jan Beulich
2021-04-13 10:18       ` Roger Pau Monné
2021-04-13 12:03         ` Jan Beulich
2021-04-13 13:03           ` Roger Pau Monné
2021-04-17 19:24   ` Tim Deegan
2021-04-19 11:25     ` Jan Beulich
2021-04-22  7:42       ` Tim Deegan
2021-04-22  9:38         ` Jan Beulich
2021-04-22 15:05           ` Tim Deegan
2021-04-23 10:51 ` [PATCH v4 0/3] VMX APIC access page and shadow adjustments Jan Beulich
2021-04-23 10:52   ` [PATCH v4 1/3] VMX: use a single, global APIC access page Jan Beulich
2021-04-23 14:17     ` Roger Pau Monné
2021-04-23 14:42       ` Jan Beulich
2021-04-26 17:55         ` Tim Deegan
2021-04-25  1:27     ` Tian, Kevin
2021-04-26 17:53     ` Tim Deegan
2021-04-23 10:53   ` [PATCH v4 2/3] x86/shadow: re-use variables in shadow_get_page_from_l1e() Jan Beulich
2021-04-23 10:54   ` Jan Beulich [this message]
2021-04-23 11:00   ` Really v5 (was: [PATCH v4 0/3] VMX APIC access page and shadow adjustments) Jan Beulich

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