Nitin A Kamble wrote:
"Unrestricted Guest" feature is added in the VMX specification.
Intel Westmere and onwards processors will support this feature.
It allows kvm guests to run real mode and unpaged mode
code natively in the VMX mode when EPT is turned on. With the
unrestricted guest there is no need to emulate the guest real mode code
in the vm86 container or in the emulator. Also the guest big real mode
code works like native.
The attached patch enhances KVM to use the unrestricted guest feature
if available on the processor. It also adds a new kernel/module
parameter to disable the unrestricted guest feature at the boot time.
@@ -1431,6 +1447,9 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
unsigned long flags;
struct vcpu_vmx *vmx = to_vmx(vcpu);
+ if (enable_unrestricted_guest)
+ goto continue_rmode;
+
I think you should just return here. You don't need to reset the mmu
context or run the init_rmode() code. Maybe you need to flush the tlb.
+
+ if (enable_unrestricted_guest && (seg != VCPU_SREG_LDTR))
+ ar |= 0x1; /* Accessed */
+
vmcs_write32(sf->ar_bytes, ar);
}
Please add a comment indicating it's for broken userspace that doesn't
set the A bit.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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