linux-kernel - Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)

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Date:   Thu, 14 Mar 2019 14:12:43 +0000
From:   Julien Grall <julien.grall@....com>
To:     Juergen Gross <jgross@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     k.khlebnikov@...sung.com,
        Stefano Stabellini <sstabellini@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        "VMware, Inc." <pv-drivers@...are.com>,
        osstest service owner <osstest-admin@...project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, Julien Freche <jfreche@...are.com>,
        Nadav Amit <namit@...are.com>, xen-devel@...ts.xenproject.org
Subject: Re: [Xen-devel] xen: Can't insert balloon page into VM userspace (WAS
 Re: [linux-linus bisection] complete test-arm64-arm64-xl-xsm)

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