Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region

[Peter Xu <peterx@redhat.com>]

On Thu, Jul 18, 2024 at 09:50:31AM +0800, Yan Zhao wrote:
> Ok. Then if we have two sets of pfns, then we can
> 1. Call remap_pfn_range() in mmap() for pfn set 1.

I don't think this will work..  At least from the current implementation,
remap_pfn_range() will only reserve the memtype if the range covers the
whole vma.

> 2. Export track_pfn_remap() and call track_pfn_remap() in mmap() for pfn
>    set 2.
> 3. Unmap and call vmf_insert_pfn() in the fault handler to map pfn set 2.

IMO this should be the similar case of MMIO being disabled on the bar,
where we can use track_pfn_remap() to register the whole vma in mmap()
first. Then in this case if you prefer proactive injection of partial of
the pfn mappings, one can do that via vmf_insert_pfn*() in mmap() after the
memtype registered.

> 
> However, I'm not sure if we can properly untrack both pfn sets 1 and 2.

Untrack should so far only happen per-vma, AFAIU, so "set 1+2" need to be
done together as they belong to the same vma.

> 
> By exporting untrack_pfn() too? Or, you'll leave VFIO to use ioremap/iounmap()
> (or the variants) to reserve memtype by itself?

Thanks,

-- 
Peter Xu