Re: [PATCH][4.15] x86: mirror compat argument translation area for 32-bit PV

["Roger Pau Monné" <roger.pau@citrix.com>]

On Mon, Feb 22, 2021 at 12:35:21PM +0100, Roger Pau Monné wrote:
> On Mon, Feb 22, 2021 at 11:27:07AM +0100, Jan Beulich wrote:
> > Now that we guard the entire Xen VA space against speculative abuse
> > through hypervisor accesses to guest memory, the argument translation
> > area's VA also needs to live outside this range, at least for 32-bit PV
> > guests. To avoid extra is_hvm_*() conditionals, use the alternative VA
> > uniformly.
> 
> Since you are double mapping the per-domain virtual area, won't it
> make more sense to map it just once outside of the Xen virtual space
> area? (so it's always using PML4_ADDR(511))

Right, that's not possible for PV 64bit domains because it's guest
owned linear address space in that case.

It seems like paravirt_ctxt_switch_to will modify the root_pgt to set
the PERDOMAIN_VIRT_START entry, does the same need to be done for
PERDOMAIN2_VIRT_START?

I would also consider giving the slot a more meaningful name, as
PERDOMAIN2_VIRT_START makes it seem like a new per-domain scratch
space, when it's just a different mapping of the existing physical
memory.

Maybe PERDOMAIN_MIRROR_VIRT_START? Or PERDOMAIN_XLAT_VIRT_START?

Thanks, Roger.