Re: [PATCH] Call SetVirtualAddressMap() by default

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Thu, Feb 23, 2023 at 11:16:28AM +0100, Jan Beulich wrote:
> On 22.02.2023 20:14, Demi Marie Obenour wrote:
> > To quote Andrew Cooper:
> > 
> >> I know we've had this argument before, but not calling
> >> SetVirtualAddressMap() isn't a viable option.  It's a prerequisite to
> >> function on literally millions of devices
> > 
> > Qubes OS has been shipping EFI_SET_VIRTUAL_ADDRESS_MAP for years, and I
> > believe OpenXT and EVE ship it as well. Mark EFI_SET_VIRTUAL_ADDRESS_MAP
> > as SUPPORTED and enable it by default.
> 
> This is insufficient justification. The main reason why we don't call
> it is because it can be called only once. Any entity taking over later
> (e.g. via kexec) can't do anything anymore about the virtual address
> associations once set. Hence what's needed to justify a change like
> this is an explanation of why this restriction is not really an issue
> to anyone in any case.

AFAIR from the discussion about the original patch, kexec under Xen does
not preserve runtime services working anyway, so this limitation is more
about some possible kexec implementation in the future, not actually
breaking something right now. And since Linux calls
SetVirtualAddressMap() _and_ supports kexec just fine, it's definitely
possible to design this future kexec extension to work after
SetVirtualAddressMap() too.

Relevant parts of that older discussion:
- 
https://lore.kernel.org/all/272a9354-bcb4-50a4-a251-6a453221d6e3@xxxxxxxxxx/T/#u
- https://lore.kernel.org/all/20191009235725.GT8065@mail-itl/T/#u

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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