[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen/x86: Adjust stack pointer in xen_sysexit
On 17/11/15 19:16, Andy Lutomirski wrote: > On Tue, Nov 17, 2015 at 11:12 AM, Andrew Cooper > <andrew.cooper3@xxxxxxxxxx> wrote: >> On 17/11/15 18:49, Andy Lutomirski wrote: >>> On Nov 17, 2015 6:40 AM, "Boris Ostrovsky" <boris.ostrovsky@xxxxxxxxxx> >>> wrote: >>>> On 11/16/2015 04:55 PM, H. Peter Anvin wrote: >>>>> On 11/16/15 12:22, Borislav Petkov wrote: >>>>>> Huh, so what's wrong with a jump: >>>>>> >>>>>> jmp 1f >>>>>> swapgs >>>>>> 1: >>>>>> >>>>> What is the point of that jump? >>>>> >>>>>>> If it would make you feel better, it could be X86_BUG_XENPV :-p >>>>>> That doesn't matter - I just don't want to open the flood gates on >>>>>> pseudo feature bits. >>>>>> >>>>>> hpa, what do you think? >>>>> Pseudo feature bits are fine, we already have plenty of them. They make >>>>> sense as they let us reuse a lot of infrastructure. >>>> >>>> So how about something like this? And then I think we can remove >>>> usergs_sysret32 and irq_enable_sysexit pv ops completely as noone will use >>>> them (lguest doesn't set them) >>>> >>> Looks good to me. Does Xen have any sysexit/sysret32 equivalent to >>> return to 32-bit user mode? If so, it could be worth trying to wire >>> it up by patching the jz instead of the test instruction. >> From the guests point of view, there is only hypercall_iret. > Doesn't hypercall_iret have flags that ask for different behavior, > though? (VG_syscall or whatever for the 64-bit case?) The one and only flag is VGCF_in_syscall Xen has its own logic for choosing between sysretq/sysretl if VGCF_in_syscall, but will end up on an iret path in all other circumstances. There is definitely some room for optimisation here, but in in some copious free time before that, I want to see about brining most of our asm code up into C. The vast majority of it doesn't need to be written in asm. > >>> Also, I'd prefer X86_FEATURE_XENPV. IMO "PV" means too many things to >>> too many people. >> I agree - PV on its own is too generic. >> >> An alternative might be X86_FEATURE_XEN_PV_GUEST which is very clear an >> unambiguous, although rather longer. > Works for me, too, although seeing "xen_pv_host" in the Linux cpu > features would be very strange indeed :) This makes me wonders whether the `insmod xen` project has managed to gain any traction ;) ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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