Messages in this thread | | | Subject | Re: [Xen-devel] Re: [RFC PATCH 15/33] move segment checks to subarch | From | Rusty Russell <> | Date | Wed, 19 Jul 2006 06:00:50 +1000 |
| |
On Tue, 2006-07-18 at 12:25 -0700, Chris Wright wrote: > * Rusty Russell (rusty@rustcorp.com.au) wrote: > > On Tue, 2006-07-18 at 00:00 -0700, Chris Wright wrote: > > > plain text document attachment (i386-segments) > > > We allow for the fact that the guest kernel may not run in ring 0. > > > This requires some abstraction in a few places when setting %cs or > > > checking privilege level (user vs kernel). > > > > Zach had an alternate patch for this, which didn't assume the kernel ran > > in a compile-time known ring, but is otherwise very similar. I've put > > it below for discussion (but Zach now tells me the asm parts are not > > required: Zach, can you mod this patch and comment?). > > This patch also doesn't have a compile time known ring, it's using > get_kernel_cs() because the Xen method for booting native is dynamic and > would resolve to ring 0 in that case (XENFEAT_supervisor_mode_kernel).
I was referring to the different ways the two patches figure out whether we're in user mode:
Yours: static inline int user_mode(struct pt_regs *regs) { return (regs->xcs & USER_MODE_MASK) != 0; }
Where you have for native: #define USER_MODE_MASK 3 vs Xen: #define USER_MODE_MASK 2
Zach's patch does this:
static inline int user_mode(struct pt_regs *regs) { return (regs->xcs & SEGMENT_RPL_MASK) == 3; }
I'm no x86pert, but the latter seems more generic to me (user mode is ring 3, vs. usermode is anything >= 2). Perhaps they are in fact equivalent?
Thanks! Rusty. -- Help! Save Australia from the worst of the DMCA: http://linux.org.au/law
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |