[PATCH] KVM: x86: do mask out upper bits of PAE CR3

From: Paolo Bonzini
Date: Mon Jul 24 2017 - 12:59:34 EST


This reverts the change of commit f85c758dbee54cc3612a6e873ef7cecdb66ebee5,
as the behavior it modified was intended.

The VM is running in 32-bit PAE mode, and Table 4-7 of the Intel manual
says:

Table 4-7. Use of CR3 with PAE Paging
Bit Position(s) Contents
4:0 Ignored
31:5 Physical address of the 32-Byte aligned
page-directory-pointer table used for linear-address
translation
63:32 Ignored (these bits exist only on processors supporting
the Intel-64 architecture)

To placate the static checker, write the mask explicitly as an
unsigned long constant instead of using a 32-bit unsigned constant.

Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Fixes: f85c758dbee54cc3612a6e873ef7cecdb66ebee5
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 82a63c59f77b..6c97c82814c4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -597,8 +597,8 @@ bool pdptrs_changed(struct kvm_vcpu *vcpu)
(unsigned long *)&vcpu->arch.regs_avail))
return true;

- gfn = (kvm_read_cr3(vcpu) & ~31ul) >> PAGE_SHIFT;
- offset = (kvm_read_cr3(vcpu) & ~31ul) & (PAGE_SIZE - 1);
+ gfn = (kvm_read_cr3(vcpu) & 0xffffffe0ul) >> PAGE_SHIFT;
+ offset = (kvm_read_cr3(vcpu) & 0xffffffe0ul) & (PAGE_SIZE - 1);
r = kvm_read_nested_guest_page(vcpu, gfn, pdpte, offset, sizeof(pdpte),
PFERR_USER_MASK | PFERR_WRITE_MASK);
if (r < 0)
--
1.8.3.1