Commit 12cb814f authored May 07, 2011 by Takuya Yoshikawa Committed by Avi Kivity May 22, 2011

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>

parent 5ce941ee

arch/x86/kvm/paging_tmpl.h

+1 −15

Original line number	Diff line number	Diff line
		@@ -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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