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From:   KarimAllah Ahmed <karahmed@amazon.de>
To:     kvm@vger.kernel.org
Cc:     KarimAllah Ahmed <karahmed@amazon.de>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH] kvm: Map PFN-type memory regions as writable (if possible)
Date:   Wed, 17 Jan 2018 18:26:05 +0100
Message-Id: <1516209965-18614-1-git-send-email-karahmed@amazon.de>
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Sender: linux-kernel-owner@vger.kernel.org
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For EPT-violations that are triggered by a read, the pages are also mapped with
write permissions (if their memory region is also writable). That would avoid
getting yet another fault on the same page when a write occurs.

This optimization only happens when you have a "struct page" backing the memory
region. So also enable it for memory regions that do not have a "struct page".

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
---
 virt/kvm/kvm_main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 97da45e..0efb089 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1534,6 +1534,8 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
 			goto retry;
 		if (r < 0)
 			pfn = KVM_PFN_ERR_FAULT;
+		if (writable)
+			*writable = true;
 	} else {
 		if (async && vma_is_valid(vma, write_fault))
 			*async = true;
-- 
2.7.4