On Thu, Apr 16, 2020 at 05:38:07PM +0200, Geert Uytterhoeven wrote: > On Thu, Apr 16, 2020 at 2:56 PM Mark Rutland <mark.rutland@xxxxxxx> wrote: > > On Thu, Apr 16, 2020 at 01:56:58PM +0200, Geert Uytterhoeven wrote: > > > Currently the user is asked about enabling support for each and every > > > vendor-specific erratum, even when support for the specific platform is > > > not enabled. > > > > > > Fix this by adding platform dependencies to the config options > > > controlling support for vendor-specific errata. > > I'm not su1re that it makes sense to do this in general, becaose the > > ARCH_* platform symbols are about plactform/SoC support (e.g. pinctrl > > drivers), and these are (mostly) CPU-local and/or VM-visible. > > > > I think that it makes sense for those to be independent because: > > * It prevents building a minimal VM image with all (non-virtualized) > > platform support disabled, but all possible (VM-visible) errata > > options enabled. I do that occassionally for testing/analysis, and I > > can imagine this is useful for those building images that are only > > intended to be used in VMs. > > Oh, you also want to build a "generic" guest kernel, with all ARCH_* > symbols disabled. Yup! As above I do this today for building test kernels I run on a number of different hosts, and I'm aware of other use-cases (e.g. WSL2 or docker for mac) where you may want to do this to minimize the core kernel either for size or security reasons. > Let's hope a maleficent user cannot disable errata mitigations in the > guest kernel and break the host ;-) Indeed ;) For cases where a malicious guest could cause harm we've added workarounds in KVM, so unless we've missed something that shouldn't be the case. Otherwise, a guest missing these is just shooting itself in the foot. > And perhaps you do want to enable some platform-specific drivers for > VFIO pass-through? Hence having ARCH_* dependencies on those drivers > means they cannot be enabled :-( Hmm... IIRC platform device passthrough requires an corresponding VFIO platform driver in the host to handle reset and so on, but it does seem a shame to not allow the user to select a driver if they really want it. I guess there might be platform-specific PCIe drivers too, which might work with VFIO regardless. Thanks, Mark.
