On 01/17/2018 09:04 AM, Andrew Cooper wrote: > On 17/01/18 09:02, Joerg Roedel wrote: >> Hi Boris, >> >> thanks for testing this :) >> >> On Tue, Jan 16, 2018 at 09:47:06PM -0500, Boris Ostrovsky wrote: >>> On 01/16/2018 11:36 AM, Joerg Roedel wrote: >>>> +.macro SWITCH_TO_KERNEL_STACK nr_regs=0 check_user=0 >>> This (and next patch's SWITCH_TO_ENTRY_STACK) need X86_FEATURE_PTI check. >>> >>> With those macros fixed I was able to boot 32-bit Xen PV guest. >> Hmm, on bare metal the stack switch happens regardless of the >> X86_FEATURE_PTI feature being set, because we always program tss.sp0 >> with the systenter stack. How is the kernel entry stack setup on xen-pv? >> I think something is missing there instead. > There is one single stack registered with Xen, on which you get a normal > exception frame in all cases, even via the registered (virtual) > syscall/sysenter/failsafe handlers. And so the check should be at least against X86_FEATURE_XENPV, not necessarily X86_FEATURE_PTI. But I guess you can still check against X86_FEATURE_PTI since without it there is not much reason to switch stacks? -boris -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
