Re: [Xen-devel] [PATCH 1/6] xen: extend XEN_DOMCTL_memory_mapping to handle cacheability

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 4/17/19 10:12 PM, Stefano Stabellini wrote:
> On Wed, 27 Feb 2019, Jan Beulich wrote:
> > > > > On 27.02.19 at 00:07, <sstabellini@xxxxxxxxxx> wrote:
> > > --- a/xen/include/public/domctl.h
> > > +++ b/xen/include/public/domctl.h
> > > @@ -571,12 +571,14 @@ struct xen_domctl_bind_pt_irq {
> > >   */
> > >   #define DPCI_ADD_MAPPING         1
> > >   #define DPCI_REMOVE_MAPPING      0
> > > +#define CACHEABILITY_DEVMEM      0 /* device memory, the default */
> > > +#define CACHEABILITY_MEMORY      1 /* normal memory */
> > >   struct xen_domctl_memory_mapping {
> > >       uint64_aligned_t first_gfn; /* first page (hvm guest phys page) in range 
> > > */
> > >       uint64_aligned_t first_mfn; /* first page (machine page) in range */
> > >       uint64_aligned_t nr_mfns;   /* number of pages in range (>0) */
> > >       uint32_t add_mapping;       /* add or remove mapping */
> > > -    uint32_t padding;           /* padding for 64-bit aligned structure */
> > > +    uint32_t cache_policy;      /* cacheability of the memory mapping */
> > >   };
> > I don't think DEVMEM and MEMORY are anywhere near descriptive
> > enough, nor - if we want such control anyway - flexible enough. I
> > think what you want is to actually specify cachability, allowing on
> > x86 to e.g. map frame buffers or alike WC. The attribute then
> > would (obviously and necessarily) be architecture specific.
> Yes, I agree with what you wrote, and also with what Julien wrote. Now
> the question is how do you both think this should look like in more
> details:
>
> - are you OK with using memory_policy instead of cache_policy like
>    Julien's suggested as name for the field?
> - are you OK with using #defines for the values?
> - should the #defines for both x86 and Arm be defined here or in other
>    headers?
> - what values would you like to see for x86?
>
> For Arm, the ones I care about are:
>
> - p2m_mmio_direct_dev
> - p2m_mmio_direct_c
First step first. What are the reason to have p2m_mmio_direct_c? Is it 
only for memory sharing between DomU and Dom0?
Cheers,

--
Julien Grall

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