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Re: [PATCH][4.15] x86: mirror compat argument translation area for 32-bit PV
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Mon, 22 Feb 2021 15:13:28 +0100
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>
- Delivery-date: Mon, 22 Feb 2021 14:13:40 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
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