On Fri, Feb 06, 2026 at 07:29:49AM +0100, Jan Beulich wrote: > On 05.02.2026 18:27, Teddy Astie wrote: > > Many machines fail to boot if this option is disabled, as > > there are no known drawback toggling this option, enable it > > by default. > > "no known drawback" ignores why it wasn't enabled originally. Imo this > wants at least mentioning, if not discussing.
Relevant discussion was at https://lore.kernel.org/xen-devel/[email protected]/ (previous attempt at switching the default) And also, (large) part of the reason for this being off by default initially was it being close to 4.13 release: https://lore.kernel.org/xen-devel/[email protected]/ Now it's substantially earlier in the 4.22 release cycle. But yes, some note in patch description would be nice. > > --- a/xen/common/Kconfig > > +++ b/xen/common/Kconfig > > @@ -363,13 +363,14 @@ config KEXEC > > > > config EFI_SET_VIRTUAL_ADDRESS_MAP > > bool "EFI: call SetVirtualAddressMap()" if EXPERT > > + default y > > help > > Call EFI SetVirtualAddressMap() runtime service to setup memory map > > for > > further runtime services. According to UEFI spec, it isn't strictly > > necessary, but many UEFI implementations misbehave when this call is > > missing. > > > > - If unsure, say N. > > + If unsure, say Y. > > When this was added, it was actually hacked in with the aim of minimal > intrusiveness. When we now default it to on, I wonder if other changes > shouldn't be made (maybe not right in this patch, but perhaps in a > single series). For example, identity mapping (with its implied > restrictions) ought to be possible to do away with when the option is > enabled. Whether the separate EFI page tables would still be needed > also is questionable. This is an interesting question, but IMHO the current approach is safer (or rather: more reliable) - which is relevant given how many UEFI systems are not exactly spec compliant... One approach that could be tried is to mirror what Linux does, but I don't see it as necessary for flipping the default. And in fact I would rather prefer to not do that at the same time - the current approach is battle tested by several downstream projects on a large number of systems. > I further wonder whether the EXPERT dependency of the prompt wouldn't > better be dropped when flipping the default. IMO the EXPERT dependency is still relevant. This option is basically "break Xen on a large number of UEFI systems". -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab
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