[PATCH AUTOSEL for 4.14 093/161] kvm: Map PFN-type memory regions as writable (if possible)

Sasha Levin
2018-04-09T03:06:42Z

From: KarimAllah Ahmed <karahmed@amazon.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@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>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.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 d81af263f50b..4f35f0dfe681 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1434,7 +1434,8 @@ 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;
@@ -1460,6 +1461,8 @@ 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
@@ -1525,7 +1528,7 @@ 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