linux-kernel - Re: [PATCH 0/4] mm/userfaultfd: modulize memory types

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Message-ID: <aFxZUHcQh3hSraqe@x1.local>
Date: Wed, 25 Jun 2025 16:17:20 -0400
From: Peter Xu <peterx@...hat.com>
To: Nikita Kalyazin <kalyazin@...zon.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Hugh Dickins <hughd@...gle.com>, Oscar Salvador <osalvador@...e.de>,
	Michal Hocko <mhocko@...e.com>,
	David Hildenbrand <david@...hat.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Ujwal Kundur <ujwal.kundur@...il.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	James Houghton <jthoughton@...gle.com>,
	Mike Rapoport <rppt@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Axel Rasmussen <axelrasmussen@...gle.com>
Subject: Re: [PATCH 0/4] mm/userfaultfd: modulize memory types

On Wed, Jun 25, 2025 at 05:56:23PM +0100, Nikita Kalyazin wrote:
> 
> 
> On 20/06/2025 20:03, Peter Xu wrote:
> > [based on akpm/mm-new]
> > 
> > This series is an alternative proposal of what Nikita proposed here on the
> > initial three patches:
> > 
> >    https://lore.kernel.org/r/20250404154352.23078-1-kalyazin@amazon.com
> > 
> > This is not yet relevant to any guest-memfd support, but paving way for it.
> 
> Hi Peter,

Hi, Nikita,

> 
> Thanks for posting this.  I confirmed that minor fault handling was working
> for guest_memfd based on this series and looked simple (a draft based on
> mmap support in guest_memfd v7 [1]):

Thanks for the quick spin, glad to know it works. Some trivial things to
mention below..

> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 5abb6d52a375..6ddc73419724 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -5,6 +5,9 @@
>  #include <linux/pagemap.h>
>  #include <linux/anon_inodes.h>
>  #include <linux/set_memory.h>
> +#ifdef CONFIG_USERFAULTFD

This ifdef not needed, userfaultfd_k.h has taken care of all cases.

> +#include <linux/userfaultfd_k.h>
> +#endif
> 
>  #include "kvm_mm.h"
> 
> @@ -396,6 +399,14 @@ static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf)
>  		kvm_gmem_mark_prepared(folio);
>  	}
> 
> +#ifdef CONFIG_USERFAULTFD

Same here.  userfaultfd_minor() is always defined.

I'll wait for a few more days for reviewers, and likely send v2 before next
week.

Thanks,

-- 
Peter Xu