Messages in this thread | | | Date | Wed, 5 Aug 2015 16:50:33 +0100 | From | David Vrabel <> | Subject | Re: [Xen-devel] [PATCH v2 02/20] xen: Introduce a function to split a Linux page into Xen page |
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On 05/08/15 15:30, Julien Grall wrote: > Hi David, > > On 24/07/15 11:10, David Vrabel wrote: >> On 24/07/15 10:54, Julien Grall wrote: >>> On 24/07/15 10:31, David Vrabel wrote: >>>> On 09/07/15 21:42, Julien Grall wrote: >>>>> The Xen interface is always using 4KB page. This means that a Linux page >>>>> may be split across multiple Xen page when the page granularity is not >>>>> the same. >>>>> >>>>> This helper will break down a Linux page into 4KB chunk and call the >>>>> helper on each of them. >>>> [...] >>>>> --- a/include/xen/page.h >>>>> +++ b/include/xen/page.h >>>>> @@ -39,4 +39,24 @@ struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS]; >>>>> >>>>> extern unsigned long xen_released_pages; >>>>> >>>>> +typedef int (*xen_pfn_fn_t)(struct page *page, unsigned long pfn, void *data); >>>>> + >>>>> +/* Break down the page in 4KB granularity and call fn foreach xen pfn */ >>>>> +static inline int xen_apply_to_page(struct page *page, xen_pfn_fn_t fn, >>>>> + void *data) >>>> >>>> I think this should be outlined (unless you have measurements that >>>> support making it inlined). >>> >>> I don't have any performance measurements. Although, when Linux is using >>> 4KB page granularity, the loop in this helper will be dropped by the >>> helper. The code would look like: >>> >>> unsigned long pfn = xen_page_to_pfn(page); >>> >>> ret = fn(page, fn, data); >>> if (ret) >>> return ret; >>> >>> The compiler could even inline the callback (fn). So it drops 2 >>> functions call. >> >> Ok, keep it inlined. >> >>>> Also perhaps make it >>>> >>>> int xen_for_each_gfn(struct page *page, >>>> xen_gfn_fn_t fn, void *data); >>> >>> gfn standing for Guest Frame Number right? >> >> Yes. This suggestion is just changing the name to make it more obvious >> what it does. > > Thinking more about this suggestion. The callback (fn) is getting a 4K > PFN in parameter and not a GFN.
I would like only APIs that deal with 64 KiB PFNs and 4 KiB GFNs. I think having a 4 KiB "PFN" is confusing.
Can you rework this xen_for_each_gfn() to pass GFNs to fn, instead?
> This is because the balloon code seems to require having a 4K PFN in > hand in few places. For instance XENMEM_populate_physmap and > HYPERVISOR_update_va_mapping.
Ug. For an auto-xlate guest frame-list needs GFNs, for a PV guest XENMEM_populate_physmap does want PFNs (so it can fill in the M2P).
Perhaps in increase_reservation:
if (auto-xlate) frame_list[i] = page_to_gfn(page); /* Or whatever per-GFN loop you need. */ else frame_list[i] = page_to_pfn(page);
update_va_mapping takes VAs (e.g, __va(pfn << PAGE_SHIFT) could be page_to_virt(page).
Sorry for being so picky here, but the inconsistency of terminology and API misuse is already confusing and I don't want to see it get worse.
David
> > Although, I'm not sure to understand the difference between GMFN, and > GPFN in the hypercall doc. > > Regards, >
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