On 22/03/18 13:39, Wanpeng Li wrote: > 2018-03-22 20:38 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: >> On 22/03/2018 12:04, Andrew Cooper wrote: >>> We've got a Force Emulation Prefix (ud2a; .ascii "xen") for doing >>> magic. Originally, this was used for PV guests to explicitly request an >>> emulated CPUID, but I extended it to HVM guests for "emulate the next >>> instruction", after we had some guest user => guest kernel privilege >>> escalations because of incorrect emulation. >> Wanpeng, why don't you add it behind a new kvm module parameter? :) > Great point! I will have a try. Thanks Paolo and Andrew. :) Using the force emulation prefix requires intercepting #UD, which is in general a BadThing(tm) for security. Therefore, we have a build time configuration option to compile in support, and require that test systems explicitly opt into using it via a command line parameter. http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/hvm/hvm.c;h=db52312882205e65b32e587106ca795f4bfab2eb;hb=refs/heads/staging#l3741 is the general #UD intercept handler if you want a reference. (You can ignore the cross-vendor part, which is leftovers from http://developer.amd.com/wordpress/media/2012/10/CrossVendorMigration.pdf ) ~Andrew
