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author | Dongxiao Xu <dongxiao.xu@intel.com> | 2013-02-12 13:44:02 +0100 |
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committer | Dongxiao Xu <dongxiao.xu@intel.com> | 2013-02-12 13:44:02 +0100 |
commit | 485f374230d39e153d7b9786e3d0336bd52ee661 (patch) | |
tree | b7e49e47b9c297b59186c5d5288edd98e01a30a4 | |
parent | 1e6275a95d3e35a72939b588f422bb761ba82f6b (diff) | |
download | xen-485f374230d39e153d7b9786e3d0336bd52ee661.tar.gz xen-485f374230d39e153d7b9786e3d0336bd52ee661.tar.bz2 xen-485f374230d39e153d7b9786e3d0336bd52ee661.zip |
VMX: disable SMEP feature when guest is in non-paging mode
SMEP is disabled if CPU is in non-paging mode in hardware.
However Xen always uses paging mode to emulate guest non-paging
mode with HAP. To emulate this behavior, SMEP needs to be manually
disabled when guest switches to non-paging mode.
We met an issue that, SMP Linux guest with recent kernel (enable
SMEP support, for example, 3.5.3) would crash with triple fault if
setting unrestricted_guest=0 in grub. This is because Xen uses an
identity mapping page table to emulate the non-paging mode, where
the page table is set with USER flag. If SMEP is still enabled in
this case, guest will meet unhandlable page fault and then crash.
Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
xen-unstable changeset: 26502:d1bf3b21f783
xen-unstable date: Wed Jan 30 17:17:30 UTC 2013
-rw-r--r-- | xen/arch/x86/hvm/vmx/vmx.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index b8f033646d..ca92b8640a 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -1227,6 +1227,13 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned int cr) { v->arch.hvm_vcpu.hw_cr[4] |= X86_CR4_PSE; v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_PAE; + /* + * SMEP is disabled if CPU is in non-paging mode in hardware. + * However Xen always uses paging mode to emulate guest non-paging + * mode with HAP. To emulate this behavior, SMEP needs to be + * manually disabled when guest switches to non-paging mode. + */ + v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_SMEP; } __vmwrite(GUEST_CR4, v->arch.hvm_vcpu.hw_cr[4]); __vmwrite(CR4_READ_SHADOW, v->arch.hvm_vcpu.guest_cr[4]); |