[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] [RFC] vpci: allow BAR write while mapped
On Mon Mar 17, 2025 at 12:32 PM GMT, Roger Pau Monné wrote: > On Fri, Mar 14, 2025 at 10:39:04AM +0000, Alejandro Vallejo wrote: > > On Thu Mar 13, 2025 at 5:43 PM GMT, Stewart Hildebrand wrote: > > > I think this just reinforces the need to rework the BAR mapping > > > machinery. > > > > Right. The most delicate part is dealing with races with another vCPU when > > the > > unmap-then-map operation does not complete in a single taking of the vpci > > lock > > I'd say. And that much is unavoidable, I think, because either unmapping or > > mapping might take a while. > > The original code was put together for dom0, I bet there are some > races that can lead to incomplete p2m mappings if the domain attempts > parallel manipulation of the BARs and memory decoding bits. However > there should be no case where an unexpected mfn gets mapped into the > p2m as a result of such races. > > It's fine for a domain to shot it's own foot if it attempts to do > concurrent PCI accesses to explicitly trigger races in the MMIO > mapping handling, as long as this doesn't cause issues to other > guests, and doesn't leak memory. > > Regards, Roger. It's refcounting bugs that would scare me the most. Or something similar, like having an expectation that a BAR is absent from a certain p2m when it's still present. Cheers, Alejandro
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