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[PATCH] x86/mm: Remove unnecessary mfn_valid() call from get_page_from_l1e()
- To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 27 Apr 2022 15:04:00 +0100
- Authentication-results: esa6.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Wed, 27 Apr 2022 14:05:01 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
mfn_valid() is not a trivially simple, and contains an evaluate_nospec() for
speculative defence. Avoid calling it redundantly, and just store the result
of the first call.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
xen/arch/x86/mm.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 72dbce43b13a..31b9f96dc0df 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -887,7 +887,7 @@ get_page_from_l1e(
uint32_t l1f = l1e_get_flags(l1e);
struct vcpu *curr = current;
struct domain *real_pg_owner;
- bool write;
+ bool write, valid;
if ( unlikely(!(l1f & _PAGE_PRESENT)) )
{
@@ -902,13 +902,15 @@ get_page_from_l1e(
return -EINVAL;
}
- if ( !mfn_valid(_mfn(mfn)) ||
+ valid = mfn_valid(_mfn(mfn));
+
+ if ( !valid ||
(real_pg_owner = page_get_owner_and_reference(page)) == dom_io )
{
int flip = 0;
/* Only needed the reference to confirm dom_io ownership. */
- if ( mfn_valid(_mfn(mfn)) )
+ if ( valid )
put_page(page);
/* DOMID_IO reverts to caller for privilege checks. */
--
2.11.0
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