Re: [PATCH v2 5/5] xen/memory, tools: Make init-dom0less consume XEN_DOMCTL_get_mem_map

[Henry Wang <xin.wang2@xxxxxxx>]

Hi Jan,

On 3/12/2024 1:07 AM, Jan Beulich wrote:
> I'm afraid the title doesn't really say what the patch actually means
> to achieve.
>
> On 08.03.2024 02:54, Henry Wang wrote:
> > Previous commits enable the toolstack to get the domain memory map,
> > therefore instead of hardcoding the guest magic pages region, use
> > the XEN_DOMCTL_get_mem_map domctl to get the start address of the
> > guest magic pages region. Add the (XEN)MEMF_force_heap_alloc memory
> > flags to force populate_physmap() to allocate page from domheap
> > instead of using 1:1 or static allocated pages to map the magic pages.
> A patch description wants to be (largely) self-contained. "Previous
> commits" shouldn't be mentioned; recall that the sequence in which
> patches go in is unknown to you up front. (In fact the terms "commit"
> or "patch" should be avoided altogether when describing what a patch
> does. The only valid use I can think of is when referring to commits
> already in the tree, and then typically by quoting their hash and
> title.)
Thanks for the detailed explanation. I will rewrite the title and part 
of the commit message in v3 to make it clear.
> > --- a/xen/include/public/memory.h
> > +++ b/xen/include/public/memory.h
> > @@ -41,6 +41,11 @@
> >   #define XENMEMF_exact_node(n) (XENMEMF_node(n) | XENMEMF_exact_node_request)
> >   /* Flag to indicate the node specified is virtual node */
> >   #define XENMEMF_vnode  (1<<18)
> > +/*
> > + * Flag to force populate physmap to use pages from domheap instead of 1:1
> > + * or static allocation.
> > + */
> > +#define XENMEMF_force_heap_alloc  (1<<19)
> >   #endif
> If this is for populate_physmap only, then other sub-ops need to reject
> its use.
>
> I have to admit I'm a little wary of allocating another flag here and ...
>
> > --- a/xen/include/xen/mm.h
> > +++ b/xen/include/xen/mm.h
> > @@ -205,6 +205,8 @@ struct npfec {
> >   #define  MEMF_no_icache_flush (1U<<_MEMF_no_icache_flush)
> >   #define _MEMF_no_scrub    8
> >   #define  MEMF_no_scrub    (1U<<_MEMF_no_scrub)
> > +#define _MEMF_force_heap_alloc 9
> > +#define  MEMF_force_heap_alloc (1U<<_MEMF_force_heap_alloc)
> >   #define _MEMF_node        16
> >   #define  MEMF_node_mask   ((1U << (8 * sizeof(nodeid_t))) - 1)
> >   #define  MEMF_node(n)     ((((n) + 1) & MEMF_node_mask) << _MEMF_node)
> ... here - we don't have that many left. Since other sub-ops aren't
> intended to support this flag, did you consider adding another (perhaps
> even arch-specific) sub-op instead?
Not really, I basically followed the discussion from [1] to implement 
this patch. However I understand your concern. Just want to make sure if 
I understand your suggestion correctly, by "adding another sub-op" you 
mean adding a sub-op similar as "XENMEM_populate_physmap" but only with 
executing the "else" part I want, so we can drop the use of these two 
added flags? Thanks!
[1] 
https://lore.kernel.org/xen-devel/3982ba47-6709-47e3-a9c2-e2d3b4a2d8e3@xxxxxxx/
Kind regards,
Henry

> Jan