From 12cb814f3bb35736420cc6bfc9fed7b6a9d3a828 Mon Sep 17 00:00:00 2001
From: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Date: Sat, 7 May 2011 16:31:36 +0900
Subject: [PATCH] KVM: MMU: Clean up gpte reading with copy_from_user()
When we optimized walk_addr_generic() by not using the generic guest
memory reader, we replaced copy_from_user() with get_user():
commit e30d2a170506830d5eef5e9d7990c5aedf1b0a51
KVM: MMU: Optimize guest page table walk
commit 15e2ac9a43d4d7d08088e404fddf2533a8e7d52e
KVM: MMU: Fix 64-bit paging breakage on x86_32
But as Andi pointed out later, copy_from_user() does the same as
get_user() as long as we give a constant size to it.
So we use copy_from_user() to clean up the code.
The only, noticeable, regression introduced by this is 64-bit gpte
reading on x86_32 hosts needed for PAE guests.
But this can be mitigated by implementing 8-byte get_user() for x86_32,
if needed.
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/paging_tmpl.h | 16 +---------------
1 file changed, 1 insertion(+), 15 deletions(-)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 52450a6b784f..88ca456ccd68 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -115,20 +115,6 @@ static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
return access;
}
-static int FNAME(read_gpte)(pt_element_t *pte, pt_element_t __user *ptep_user)
-{
-#if defined(CONFIG_X86_32) && (PTTYPE == 64)
- u32 *p = (u32 *)pte;
- u32 __user *p_user = (u32 __user *)ptep_user;
-
- if (unlikely(get_user(*p, p_user)))
- return -EFAULT;
- return get_user(*(p + 1), p_user + 1);
-#else
- return get_user(*pte, ptep_user);
-#endif
-}
-
/*
* Fetch a guest pte for a guest virtual address
*/
@@ -199,7 +185,7 @@ walk:
}
ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
- if (unlikely(FNAME(read_gpte)(&pte, ptep_user))) {
+ if (unlikely(copy_from_user(&pte, ptep_user, sizeof(pte)))) {
present = false;
break;
}
--
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