linux-kernel - [PATCH 3.16 083/212] arm/arm64: KVM: Enforce unconditional flush to PoC when mapping to stage-2

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Message-ID: <lsq.1496331796.993119704@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Marc Zyngier" <marc.zyngier@....com>,
        "Christoffer Dall" <christoffer.dall@...aro.org>
Subject: [PATCH 3.16 083/212] arm/arm64: KVM: Enforce unconditional flush
 to PoC when mapping to stage-2

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Marc Zyngier <marc.zyngier@....com>

commit 8f36ebaf21fdae99c091c67e8b6fab33969f2667 upstream.

When we fault in a page, we flush it to the PoC (Point of Coherency)
if the faulting vcpu has its own caches off, so that it can observe
the page we just brought it.

But if the vcpu has its caches on, we skip that step. Bad things
happen when *another* vcpu tries to access that page with its own
caches disabled. At that point, there is no garantee that the
data has made it to the PoC, and we access stale data.

The obvious fix is to always flush to PoC when a page is faulted
in, no matter what the state of the vcpu is.

Fixes: 2d58b733c876 ("arm64: KVM: force cache clean on page fault when caches are off")
Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
[bwh: Backported to 3.16: conditions for flushing were simpler here]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm/include/asm/kvm_mmu.h   | 9 +--------
 arch/arm64/include/asm/kvm_mmu.h | 3 +--
 2 files changed, 2 insertions(+), 10 deletions(-)

--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -142,8 +142,7 @@ static inline bool vcpu_has_cache_enable
 static inline void coherent_cache_guest_page(struct kvm_vcpu *vcpu, hva_t hva,
 					     unsigned long size)
 {
-	if (!vcpu_has_cache_enabled(vcpu))
-		kvm_flush_dcache_to_poc((void *)hva, size);
+	kvm_flush_dcache_to_poc((void *)hva, size);
 	
 	/*
 	 * If we are going to insert an instruction page and the icache is
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -141,8 +141,7 @@ static inline bool vcpu_has_cache_enable
 static inline void coherent_cache_guest_page(struct kvm_vcpu *vcpu, hva_t hva,
 					     unsigned long size)
 {
-	if (!vcpu_has_cache_enabled(vcpu))
-		kvm_flush_dcache_to_poc((void *)hva, size);
+	kvm_flush_dcache_to_poc((void *)hva, size);
 
 	if (!icache_is_aliasing()) {		/* PIPT */
 		flush_icache_range(hva, hva + size);