Messages in this thread |  | | Subject | Re: [RFC KVM 06/27] KVM: x86: Exit KVM isolation on IRQ entry | From | Alexandre Chartre <> | Date | Tue, 14 May 2019 09:58:04 +0200 |
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On 5/14/19 9:07 AM, Peter Zijlstra wrote: > On Mon, May 13, 2019 at 11:13:34AM -0700, Andy Lutomirski wrote: >> On Mon, May 13, 2019 at 9:28 AM Alexandre Chartre >> <alexandre.chartre@oracle.com> wrote: > >>> Actually, I am not sure this is effectively useful because the IRQ >>> handler is probably faulting before it tries to exit isolation, so >>> the isolation exit will be done by the kvm page fault handler. I need >>> to check that. >>> >> >> The whole idea of having #PF exit with a different CR3 than was loaded >> on entry seems questionable to me. I'd be a lot more comfortable with >> the whole idea if a page fault due to accessing the wrong data was an >> OOPS and the code instead just did the right thing directly. > > So I've ran into this idea before; it basically allows a lazy approach > to things. > > I'm somewhat conflicted on things, on the one hand, changing CR3 from > #PF is a natural extention in that #PF already changes page-tables (for > userspace / vmalloc etc..), on the other hand, there's a thin line > between being lazy and being sloppy. > > If we're going down this route; I think we need a very coherent design > and strong rules. >
Right. We should particularly ensure that the KVM page-table remains a subset of the kernel page-table, in particular page-table changes (e.g. for vmalloc etc...) should happen in the kernel page-table and not in the kvm page-table.
So we should probably enforce switching to the kernel page-table when doing operation like vmalloc. The current code doesn't enforce it, but I can see it faulting, when doing any allocation (because the kvm page table doesn't have all structures used during an allocation).
alex.
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