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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>,
	"Ian Jackson" <iwj@xenproject.org>
Subject: [PATCH v2 8/8] x86/PV: use get_unsafe() instead of copy_from_unsafe()
Date: Wed, 17 Feb 2021 09:23:33 +0100	[thread overview]
Message-ID: <0a59ae2f-448e-610d-e8a2-a7c3f9f3918f@suse.com> (raw)
In-Reply-To: <b466a19e-e547-3c7c-e39b-1a4c848a053a@suse.com>

The former expands to a single (memory accessing) insn, which the latter
does not guarantee. Yet we'd prefer to read consistent PTEs rather than
risking a split read racing with an update done elsewhere.

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

--- a/xen/arch/x86/pv/mm.c
+++ b/xen/arch/x86/pv/mm.c
@@ -41,9 +41,7 @@ l1_pgentry_t *map_guest_l1e(unsigned lon
         return NULL;
 
     /* Find this l1e and its enclosing l1mfn in the linear map. */
-    if ( copy_from_unsafe(&l2e,
-                          &__linear_l2_table[l2_linear_offset(linear)],
-                          sizeof(l2_pgentry_t)) )
+    if ( get_unsafe(l2e, &__linear_l2_table[l2_linear_offset(linear)]) )
         return NULL;
 
     /* Check flags that it will be safe to read the l1e. */
--- a/xen/arch/x86/pv/mm.h
+++ b/xen/arch/x86/pv/mm.h
@@ -22,9 +22,7 @@ static inline l1_pgentry_t guest_get_eff
         toggle_guest_pt(curr);
 
     if ( unlikely(!__addr_ok(linear)) ||
-         copy_from_unsafe(&l1e,
-                          &__linear_l1_table[l1_linear_offset(linear)],
-                          sizeof(l1_pgentry_t)) )
+         get_unsafe(l1e, &__linear_l1_table[l1_linear_offset(linear)]) )
         l1e = l1e_empty();
 
     if ( user_mode )



  parent reply	other threads:[~2021-02-17  8:23 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-17  8:16 [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors Jan Beulich
2021-02-17  8:19 ` [PATCH v2 1/8] x86: split __{get,put}_user() into "guest" and "unsafe" variants Jan Beulich
2021-02-17  8:20 ` [PATCH v2 2/8] x86: split __copy_{from,to}_user() " Jan Beulich
2021-02-17  8:20 ` [PATCH v2 3/8] x86/PV: harden guest memory accesses against speculative abuse Jan Beulich
2021-02-17  8:21 ` [PATCH v2 4/8] x86: rename {get,put}_user() to {get,put}_guest() Jan Beulich
2021-02-22 15:22   ` Roger Pau Monné
2021-02-17  8:21 ` [PATCH v2 5/8] x86/gdbsx: convert "user" to "guest" accesses Jan Beulich
2021-02-22 15:31   ` Roger Pau Monné
2021-02-22 15:55     ` Jan Beulich
2021-02-22 16:08       ` Roger Pau Monné
2021-02-17  8:22 ` [PATCH v2 6/8] x86: rename copy_{from,to}_user() to copy_{from,to}_guest_pv() Jan Beulich
2021-02-23 11:04   ` Roger Pau Monné
2021-02-23 15:15     ` Jan Beulich
2021-02-17  8:22 ` [PATCH v2 7/8] x86: move stac()/clac() from {get,put}_unsafe_asm() Jan Beulich
2021-02-23 11:40   ` Roger Pau Monné
2021-02-17  8:23 ` Jan Beulich [this message]
2021-02-23 11:59   ` [PATCH v2 8/8] x86/PV: use get_unsafe() instead of copy_from_unsafe() Roger Pau Monné
2021-02-23 15:25     ` Jan Beulich
2021-02-23 15:37       ` Roger Pau Monné
2021-02-23 16:13         ` Jan Beulich
2021-02-23 18:03           ` Roger Pau Monné
2021-02-19 15:50 ` [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors Ian Jackson
2021-02-19 15:56   ` Jan Beulich
2021-02-19 16:13     ` Ian Jackson
2021-02-19 16:16       ` Jan Beulich
2021-02-19 16:30         ` Ian Jackson
2021-02-24 11:13   ` Jan Beulich
2021-02-24 13:08     ` Ian Jackson
2021-02-24 13:18       ` Jan Beulich
2021-02-24 13:26         ` Ian Jackson

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