Messages in this thread | | | Subject | Re: [kvm-devel] [PATCH 2/3] Refactor hypercall infrastructure | From | Anthony Liguori <> | Date | Wed, 29 Aug 2007 00:51:10 -0500 |
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On Wed, 2007-08-29 at 04:12 +1000, Rusty Russell wrote: > On Mon, 2007-08-27 at 10:16 -0500, Anthony Liguori wrote: > > This patch refactors the current hypercall infrastructure to better support live > > migration and SMP. It eliminates the hypercall page by trapping the UD > > exception that would occur if you used the wrong hypercall instruction for the > > underlying architecture and replacing it with the right one lazily. > > It also reduces the number of hypercall args, which you don't mention > here.
Oh yes, sorry.
> > + er = emulate_instruction(&svm->vcpu, kvm_run, 0, 0); > > + > > + /* we should only succeed here in the case of hypercalls which > > + cannot generate an MMIO event. MMIO means that the emulator > > + is mistakenly allowing an instruction that should generate > > + a UD fault so it's a bug. */ > > + BUG_ON(er == EMULATE_DO_MMIO); > > This seems... unwise. Firstly we know our emulator is incomplete. > Secondly an SMP guest can exploit this to crash the host.
This code is gone in v2.
> (Code is in two places). > > > +#define KVM_HYPERCALL ".byte 0x0f,0x01,0xc1"
Good point.
> A nice big comment would be nice here, I think. Note that this is big > enough for both "int $0x1f" and "sysenter", so I'm happy.
I need to add a comment somewhere mentioning that if you patch with something less than 3 bytes, then you should pad with nop but the hypervisor must treat the whole instruction (including the padding) as atomic (that is, regardless of hypercall size, eip += 3) or you run the risk of breakage during migration.
Regards,
Anthony Liguori
> Cheers, > Rusty. > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Splunk Inc. > Still grepping through log files to find problems? Stop. > Now Search log events and configuration files using AJAX and a browser. > Download your FREE copy of Splunk now >> http://get.splunk.com/ > _______________________________________________ > kvm-devel mailing list > kvm-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/kvm-devel
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