Re: [Xen-devel] [PATCH RFC v2 07/12] x86: allow per-domain mappings without NX bit or with specific mfn

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.01.18 at 13:32, <jgross@xxxxxxxx> wrote:
> For support of per-vcpu stacks we need per-vcpu trampolines. To be
> able to put those into the per-domain mappings the upper levels
> page tables must not have NX set for per-domain mappings.
> 
> In order to be able to reset the NX bit for a per-domain mapping add
> a helper flipflags_perdomain_mapping() for flipping page table flags
> of a specific mapped page.
> 
> To be able to use a page from xen heap for the last per-vcpu stack
> page add a helper to map an arbitrary mfn in the perdomain area.

One further remark on this patch as a whole:
create_perdomain_mapping() allows the L1 tables to be returned,
and I think making this fit your needs (if it doesn't in its current
shape) might be better than introducing new functions which in
the end only want to fiddle with the L1 entries of previously
established mappings. This might also help mapping the pCPU's
GDT into the vCPU's per-domain mappings during context switch,
as suggested elsewhere.

Jan


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