linux-kernel - [PATCH v2 4/5] mmu: change unconditional setting of the u bit in fault bitmap

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Date:	Tue, 12 Jul 2016 18:18:51 -0400
From:	Bandan Das <bsd@...hat.com>
To:	kvm@...r.kernel.org
Cc:	pbonzini@...hat.com, guangrong.xiao@...ux.intel.com,
	kernellwp@...il.com, linux-kernel@...r.kernel.org
Subject: [PATCH v2 4/5] mmu: change unconditional setting of the u bit in fault bitmap

For the nested EPT case, we assume that the read bit (u) is
always set since we used to unconditionally set it in set_spte().
Modify it to only be set when host ept execute only support
isn't present.

Signed-off-by: Bandan Das <bsd@...hat.com>
---
 arch/x86/kvm/mmu.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c364dcb..566eea5 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3923,9 +3923,10 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu,
 				 *   clearer.
 				 */
 				smap = cr4_smap && u && !uf && !ff;
-			} else
-				/* Not really needed: no U/S accesses on ept  */
-				u = 1;
+			} else {
+				if (shadow_present_mask)
+					u = 1;
+			}
 
 			fault = (ff && !x) || (uf && !u) || (wf && !w) ||
 				(smapf && smap);
-- 
2.5.5