kvm: Map PFN-type memory regions as writable (if possible)

Web:        https://git.kernel.org/torvalds/c/a340b3e229b24a56f1c7f5826b15a3af0f4b13e5
Commit:     a340b3e229b24a56f1c7f5826b15a3af0f4b13e5
Parent:     e53175395d7e12d8474707271bc02a2814279843
Refname:    refs/heads/master
Author:     KarimAllah Ahmed <[email protected]>
AuthorDate: Wed Jan 17 19:18:56 2018 +0100
Committer:  Radim Krčmář <[email protected]>
CommitDate: Wed Jan 31 18:25:33 2018 +0100

    kvm: Map PFN-type memory regions as writable (if possible)
    
    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 <[email protected]>
    Cc: Radim Krčmář <[email protected]>
    Cc: [email protected]
    Cc: [email protected]
    Signed-off-by: KarimAllah Ahmed <[email protected]>
    Reviewed-by: Paolo Bonzini <[email protected]>
    Signed-off-by: Radim Krčmář <[email protected]>
---
 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 b4414842b023..8af42eab126d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1428,7 +1428,8 @@ 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;
@@ -1454,6 +1455,8 @@ 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
@@ -1519,7 +1522,7 @@ 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)
--
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