40 lines
1.8 KiB
Diff
40 lines
1.8 KiB
Diff
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# HG changeset patch
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# User Dongxiao Xu <dongxiao.xu@intel.com>
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# Date 1359566250 28800
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# Node ID d1bf3b21f78302dad1ed53e540facf7b9a0e2ab5
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# Parent 8201b6ec3564c80db5516cdcf36dcfa9b7fdd93b
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VMX: disable SMEP feature when guest is in non-paging mode
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SMEP is disabled if CPU is in non-paging mode in hardware.
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However Xen always uses paging mode to emulate guest non-paging
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mode with HAP. To emulate this behavior, SMEP needs to be manually
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disabled when guest switches to non-paging mode.
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We met an issue that, SMP Linux guest with recent kernel (enable
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SMEP support, for example, 3.5.3) would crash with triple fault if
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setting unrestricted_guest=0 in grub. This is because Xen uses an
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identity mapping page table to emulate the non-paging mode, where
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the page table is set with USER flag. If SMEP is still enabled in
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this case, guest will meet unhandlable page fault and then crash.
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Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
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Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
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Committed-by: Keir Fraser <keir@xen.org>
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--- a/xen/arch/x86/hvm/vmx/vmx.c
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+++ b/xen/arch/x86/hvm/vmx/vmx.c
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@@ -1227,6 +1227,13 @@ static void vmx_update_guest_cr(struct v
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{
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v->arch.hvm_vcpu.hw_cr[4] |= X86_CR4_PSE;
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v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_PAE;
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+ /*
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+ * SMEP is disabled if CPU is in non-paging mode in hardware.
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+ * However Xen always uses paging mode to emulate guest non-paging
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+ * mode with HAP. To emulate this behavior, SMEP needs to be
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+ * manually disabled when guest switches to non-paging mode.
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+ */
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+ v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_SMEP;
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}
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__vmwrite(GUEST_CR4, v->arch.hvm_vcpu.hw_cr[4]);
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__vmwrite(CR4_READ_SHADOW, v->arch.hvm_vcpu.guest_cr[4]);
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