[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] xen: Remove config dependency in XEN_PRIVCMD definition
On Wed, 9 Oct 2024, Jan Beulich wrote: > On 09.10.2024 08:20, Jiqian Chen wrote: > > Commit 2fae6bb7be32 ("xen/privcmd: Add new syscall to get gsi from dev") > > adds a weak reverse dependency to the config XEN_PRIVCMD definition, its > > purpose is to pass the combination of compilation that CONFIG_XEN_PRIVCMD=y > > and CONFIG_XEN_PCIDEV_BACKEND=m, because in that combination, xen-pciback > > is compiled as a module but xen-privcmd is built-in, so xen-privcmd can't > > find the implementation of pcistub_get_gsi_from_sbdf. > > > > But that dependency causes xen-privcmd can't be loaded on domU, because > > dependent xen-pciback is always not be loaded successfully on domU. > > > > To solve above problem and cover original commit's requirement, just remove > > that dependency, because the code "IS_REACHABLE(CONFIG_XEN_PCIDEV_BACKEND)" > > of original commit is enough to meet the requirement. > > > > Fixes: 2fae6bb7be32 ("xen/privcmd: Add new syscall to get gsi from dev") > > Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx> > > This lacks a Reported-by:. > > > --- a/drivers/xen/Kconfig > > +++ b/drivers/xen/Kconfig > > @@ -261,7 +261,6 @@ config XEN_SCSI_BACKEND > > config XEN_PRIVCMD > > tristate "Xen hypercall passthrough driver" > > depends on XEN > > - imply XEN_PCIDEV_BACKEND > > default m > > help > > The hypercall passthrough driver allows privileged user programs to > > The report wasn't about a build problem, but a runtime one. Removing the > dependency here doesn't change anything in the dependency of xen-privcmd > on xen-pciback, as the use of pcistub_get_gsi_from_sbdf() continues to > exist. > > Consider the case of XEN_PCIDEV_BACKEND=m and XEN_PRIVCMD=m, which > I guess is what Marek is using in his config. Both drivers are available > in such a configuration, yet loading of xen-privcmd then requires to > load xen-pciback first. And that latter load attempt will fail in a DomU. > The two drivers simply may not have any dependency in either direction. The idea is that there should be no hard dependency on pcistub_get_gsi_from_sbdf(). If it is available, the service will be used, otherwise an error will be reported. The problem is that IS_REACHABLE is a compile-time check. What we need is a runtime check instead. Maybe symbol_get or try_module_get ?
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