Re: [PATCH for-4.14 v3] mm: fix public declaration of struct xen_mem_acquire_resource

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.06.2020 17:39, Roger Pau Monne wrote:
> XENMEM_acquire_resource and it's related structure is currently inside
> a __XEN__ or __XEN_TOOLS__ guarded section to limit it's scope to the
> hypervisor or the toolstack only. This is wrong as the hypercall is
> already being used by the Linux kernel at least, and as such needs to
> be public.
> 
> Also switch the usage of uint64_aligned_t to plain uint64_t, as
> uint64_aligned_t is only to be used by the toolstack. Doing such
> change will reduce the size of the structure on 32bit x86 by 4bytes,
> since there will be no padding added after the frame_list handle.
> 
> This is fine, as users of the previous layout will allocate 4bytes of
> padding that won't be read by Xen, and users of the new layout won't
> allocate those, which is also fine since Xen won't try to access them.
> 
> Note that the structure already has compat handling, and such handling
> will take care of copying the right size (ie: minus the padding) when
> called from a 32bit x86 context. This is true for the compat code both
> before and after this patch, since the structures in the memory.h
> compat header are subject to a pragma pack(4), which already removed
> the trailing padding that would otherwise be introduced by the
> alignment of the frame field to 8 bytes.
> 
> Fixes: 3f8f12281dd20 ('x86/mm: add HYPERVISOR_memory_op to acquire guest 
> resources')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>