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

From: Henry Wang <xin.wang2@amd.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Wei Liu <wl@xen.org>, Anthony PERARD <anthony.perard@citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Alec Kwapis <alec.kwapis@medtronic.com>,
	<xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v2 5/5] xen/memory, tools: Make init-dom0less consume XEN_DOMCTL_get_mem_map
Date: Fri, 29 Mar 2024 13:11:35 +0800	[thread overview]
Message-ID: <b1393dbe-42c2-4839-8ca3-7dc71fe72969@amd.com> (raw)
In-Reply-To: <1cb8bca3-58b6-4a8d-ac46-8338ea5807e7@suse.com>

Hi Jan,

On 3/12/2024 1:07 AM, Jan Beulich wrote:
>> +/*
>> + * 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?

While revisiting this comment when trying to come up with a V3, I 
realized adding a sub-op here in the same level as 
XENMEM_populate_physmap will basically duplicate the function 
populate_physmap() with just the "else" (the non-1:1 allocation) part, 
also a similar xc_domain_populate_physmap_exact() & co will be needed 
from the toolstack side to call the new sub-op. So I am having the 
concern of the duplication of code and not sure if I understand you 
correctly. Would you please elaborate a bit more or clarify if I 
understand you correctly? Thanks!

Kind regards,
Henry

> Jan