linux-kernel - [PATCH AUTOSEL for 4.15 113/189] kvm: Map PFN-type memory regions as writable (if possible)

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Date:   Mon, 9 Apr 2018 00:18:15 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     KarimAllah Ahmed <karahmed@...zon.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.15 113/189] kvm: Map PFN-type memory regions as
 writable (if possible)

From: KarimAllah Ahmed <karahmed@...zon.de>

[ Upstream commit a340b3e229b24a56f1c7f5826b15a3af0f4b13e5 ]

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@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 virt/kvm/kvm_main.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e536977e7b6d..234d03abcb75 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1433,7 +1433,8 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)
 
 static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 			       unsigned long addr, bool *async,
-			       bool write_fault, kvm_pfn_t *p_pfn)
+			       bool write_fault, bool *writable,
+			       kvm_pfn_t *p_pfn)
 {
 	unsigned long pfn;
 	int r;
@@ -1459,6 +1460,8 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 
 	}
 
+	if (writable)
+		*writable = true;
 
 	/*
 	 * Get a reference here because callers of *hva_to_pfn* and
@@ -1524,7 +1527,7 @@ retry:
 	if (vma == NULL)
 		pfn = KVM_PFN_ERR_FAULT;
 	else if (vma->vm_flags & (VM_IO | VM_PFNMAP)) {
-		r = hva_to_pfn_remapped(vma, addr, async, write_fault, &pfn);
+		r = hva_to_pfn_remapped(vma, addr, async, write_fault, writable, &pfn);
 		if (r == -EAGAIN)
 			goto retry;
 		if (r < 0)
-- 
2.15.1