linux-kernel - Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory

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Date:   Fri, 24 Feb 2023 13:42:56 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Alexey Kardashevskiy <aik@....com>
Cc:     Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to
 create restricted user memory

> > int restrictedmem_bind(struct file *file, pgoff_t start, pgoff_t end,
> > 		       struct restrictedmem_notifier *notifier, bool exclusive)
> > {
> > 	struct restrictedmem *rm = file->f_mapping->private_data;
> > 	int ret = -EINVAL;
> > 
> > 	down_write(&rm->lock);
> > 
> > 	/* Non-exclusive mappings are not yet implemented. */
> > 	if (!exclusive)
> > 		goto out_unlock;
> > 
> > 	if (!xa_empty(&rm->bindings)) {
> > 		if (exclusive != rm->exclusive)
> > 			goto out_unlock;
> > 
> > 		if (exclusive && xa_find(&rm->bindings, &start, end, XA_PRESENT))
> > 			goto out_unlock;
> > 	}
> > 
> > 	xa_store_range(&rm->bindings, start, end, notifier, GFP_KERNEL);
> 
> 
> || ld: mm/restrictedmem.o: in function `restrictedmem_bind':
> mm/restrictedmem.c|295| undefined reference to `xa_store_range'

Right, xa_store_range() is only available for XARRAY_MULTI.

> 
> 
> This is missing:
> ===
> diff --git a/mm/Kconfig b/mm/Kconfig
> index f952d0172080..03aca542c0da 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1087,6 +1087,7 @@ config SECRETMEM
>  config RESTRICTEDMEM
>         bool
>         depends on TMPFS
> +       select XARRAY_MULTI
> ===
> 
> Thanks,
> 
> 
> 
> > 	rm->exclusive = exclusive;
> > 	ret = 0;
> > out_unlock:
> > 	up_write(&rm->lock);
> > 	return ret;
> > }
> > EXPORT_SYMBOL_GPL(restrictedmem_bind);
> > 
> > void restrictedmem_unbind(struct file *file, pgoff_t start, pgoff_t end,
> > 			  struct restrictedmem_notifier *notifier)
> > {
> > 	struct restrictedmem *rm = file->f_mapping->private_data;
> > 
> > 	down_write(&rm->lock);
> > 	xa_store_range(&rm->bindings, start, end, NULL, GFP_KERNEL);
> > 	synchronize_rcu();
> > 	up_write(&rm->lock);
> > }
> > EXPORT_SYMBOL_GPL(restrictedmem_unbind);
> 
> -- 
> Alexey