linux-kernel - Re: [PATCH v4 01/12] mm/shmem: Introduce F_SEAL

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Date:   Thu, 17 Feb 2022 20:56:57 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        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>,
        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>,
        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
Subject: Re: [PATCH v4 01/12] mm/shmem: Introduce F_SEAL_INACCESSIBLE

On Mon, Feb 07, 2022 at 01:24:42PM +0100, Vlastimil Babka wrote:
> On 1/18/22 14:21, Chao Peng wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > 
> >  /*
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index 18f93c2d68f1..72185630e7c4 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -1098,6 +1098,13 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
> >  		    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
> >  			return -EPERM;
> >  
> > +		if (info->seals & F_SEAL_INACCESSIBLE) {
> > +			if(i_size_read(inode))
> 
> Is this needed? The rest of the function seems to trust oldsize obtained by
> plain reading inode->i_size well enough, so why be suddenly paranoid here?

oldsize sounds enough here, unless kirill has different mind.

> 
> > +				return -EPERM;
> > +			if (newsize & ~PAGE_MASK)
> > +				return -EINVAL;
> > +		}
> > +
> >  		if (newsize != oldsize) {
> >  			error = shmem_reacct_size(SHMEM_I(inode)->flags,
> > +		if ((info->seals & F_SEAL_INACCESSIBLE) &&
> > +		    (offset & ~PAGE_MASK || len & ~PAGE_MASK)) {
> 
> Could we use PAGE_ALIGNED()?

Yes, definitely, thanks.

Chao
> 
> > +			error = -EINVAL;
> > +			goto out;
> > +		}
> > +
> >  		shmem_falloc.waitq = &shmem_falloc_waitq;
> >  		shmem_falloc.start = (u64)unmap_start >> PAGE_SHIFT;
> >  		shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;