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Date:   Fri, 21 Jul 2023 15:33:15 -0700
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Subject: Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for
 guest-specific backing memory
From:   Sean Christopherson <seanjc@google.com>
To:     Isaku Yamahata <isaku.yamahata@gmail.com>
Cc:     Yuan Yao <yuan.yao@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anup Patel <anup@brainfault.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Fuad Tabba <tabba@google.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Vishal Annapurve <vannapurve@google.com>,
        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Wang <wei.w.wang@intel.com>,
        Liam Merwick <liam.merwick@oracle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
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On Fri, Jul 21, 2023, Isaku Yamahata wrote:
> On Fri, Jul 21, 2023 at 02:13:14PM +0800,
> Yuan Yao <yuan.yao@linux.intel.com> wrote:
> > > +static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
> > > +{
> > > +	struct list_head *gmem_list = &mapping->private_list;
> > > +	struct kvm_memory_slot *slot;
> > > +	struct kvm_gmem *gmem;
> > > +	unsigned long index;
> > > +	pgoff_t start, end;
> > > +	gfn_t gfn;
> > > +
> > > +	filemap_invalidate_lock_shared(mapping);
> > > +
> > > +	start = page->index;
> > > +	end = start + thp_nr_pages(page);
> > > +
> > > +	list_for_each_entry(gmem, gmem_list, entry) {
> > > +		xa_for_each_range(&gmem->bindings, index, slot, start, end - 1) {
> > > +			for (gfn = start; gfn < end; gfn++) {
> > 
> > Why the start end range used as gfn here ?

Math is hard?  I almost always mess up these types of things, and then catch my
bugs via tests.  But I don't have tests for this particular flow...   Which
reminds me, we need tests for this :-)  Hopefully error injection provides most
of what we need?

> > the page->index is offset of inode's page cache mapping and
> > gmem address space, IIUC, gfn calculation should follow same
> > way as kvm_gmem_invalidate_begin().
> 
> Also instead of sending signal multiple times, we can utilize lsb argument.

As Vishal pointed out, this code shouldn't be sending signals in the first place.