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Subject: Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS
 Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)
To:     Juergen Gross <jgross@suse.com>,
        David Hildenbrand <david@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Matthew Wilcox <willy@infradead.org>
Cc:     k.khlebnikov@samsung.com,
        Stefano Stabellini <sstabellini@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        "VMware, Inc." <pv-drivers@vmware.com>,
        osstest service owner <osstest-admin@xenproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org, Julien Freche <jfreche@vmware.com>,
        Nadav Amit <namit@vmware.com>, xen-devel@lists.xenproject.org
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 <45323ea0-2a50-8891-830e-e1f8a8ed23ea@citrix.com>
 <f4b40d91-9c41-60ed-6b4e-df47af8e5292@oracle.com>
 <9a40e1ff-7605-e822-a1d2-502a12d0fba7@redhat.com>
 <6f8aca6c-355b-7862-75aa-68fe566f76fb@redhat.com>
 <ec71c03e-987d-2b73-9fe6-2604a3c32017@suse.com>
From:   Julien Grall <julien.grall@arm.com>
Message-ID: <cb525882-b52f-c142-8a6a-e5cb491e05d0@arm.com>
Date:   Thu, 14 Mar 2019 14:12:43 +0000
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Hi,

On 3/14/19 8:37 AM, Juergen Gross wrote:
> On 12/03/2019 20:46, David Hildenbrand wrote:
>> On 12.03.19 19:23, David Hildenbrand wrote:
>>
>> I guess something like this could do the trick if I understood it correctly:
>>
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index 39b229f9e256..d37dd5bb7a8f 100644
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -604,6 +604,7 @@ int alloc_xenballooned_pages(int nr_pages, struct
>> page **pages)
>>          while (pgno < nr_pages) {
>>                  page = balloon_retrieve(true);
>>                  if (page) {
>> +                       __ClearPageOffline(page);
>>                          pages[pgno++] = page;
>>   #ifdef CONFIG_XEN_HAVE_PVMMU
>>                          /*
>> @@ -645,8 +646,10 @@ void free_xenballooned_pages(int nr_pages, struct
>> page **pages)
>>          mutex_lock(&balloon_mutex);
>>
>>          for (i = 0; i < nr_pages; i++) {
>> -               if (pages[i])
>> +               if (pages[i]) {
>> +                       __SetPageOffline(pages[i]);
>>                          balloon_append(pages[i]);
>> +               }
>>          }
>>
>>          balloon_stats.target_unpopulated -= nr_pages;
>>
>>
>> At least this way, the pages allocated (and thus eventually mapped to
>> user space) would not be marked, but the other ones would remain marked
>> and could be excluded by makedumptool.
>>
> 
> I think this patch should do the trick. Julien, could you give it a
> try? On x86 I can't reproduce your problem easily as dom0 is PV with
> plenty of unpopulated pages for grant memory not suffering from
> missing "offline" bit.

Sure. I managed to get the console working with the patch suggested by 
David. Feel free to add my tested-by if when you resend it as is.

Cheers,

-- 
Julien Grall