From: Jan Beulich <jbeulich@suse.com>
To: Julien Grall <julien@xen.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Ian Jackson <iwj@xenproject.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Charles Chiou <cchiou@ambarella.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: dom0less boot two compressed kernel images out-of-memory work-around
Date: Thu, 4 Mar 2021 09:34:45 +0100 [thread overview]
Message-ID: <511603c8-40b4-5e22-7eba-7722d89895fe@suse.com> (raw)
In-Reply-To: <58aaf68f-4499-9400-6eb2-f1ad3b620c73@xen.org>
On 03.03.2021 20:36, Julien Grall wrote:
> (BCCing xen-users, CCing xen-devel + a few folks)
>
> Hi,
>
> Moving the discussion to xen-devel.
>
> On 22/02/2021 05:02, Charles Chiou wrote:
>> When trying to boot two zImage using dom0less boot on ARM, we encountered this problem when xen runs gunzip on second guest:
>>
>> (XEN) ****************************************
>> (XEN) Panic on CPU 0:
>> (XEN) Out of memory
>> (XEN) ****************************************
>>
>> And worked around it with the following patch. We'd like to check to see if this is a known issue and if the work-around looks reasonable. Thank you
>
> I haven't seen any similar report in the past.
>
>>
>>
>> diff --git a/xen/common/gunzip.c b/xen/common/gunzip.c
>> index db4efcd34b..e5bd19ba7f 100644
>> --- a/xen/common/gunzip.c
>> +++ b/xen/common/gunzip.c
>> @@ -113,8 +113,10 @@ __init int perform_gunzip(char *output, char *image, unsigned long image_len)
>>
>> window = (unsigned char *)output;
>>
>> + if (!free_mem_ptr) {
>> free_mem_ptr = (unsigned long)alloc_xenheap_pages(HEAPORDER, 0);
>> free_mem_end_ptr = free_mem_ptr + (PAGE_SIZE << HEAPORDER);
>> + }
>>
>> inbuf = (unsigned char *)image;
>> insize = image_len;
>> @@ -131,7 +133,12 @@ __init int perform_gunzip(char *output, char *image, unsigned long image_len)
>> rc = 0;
>> }
>>
>> + if (free_mem_ptr) {
>> free_xenheap_pages((void *)free_mem_ptr, HEAPORDER);
>> + free_mem_ptr = 0;
>> + }
>> +
>> + bytes_out = 0;
>>
>> return rc;
>> }
>> diff --git a/xen/common/inflate.c b/xen/common/inflate.c
>> index f99c985d61..de96002188 100644
>> --- a/xen/common/inflate.c
>> +++ b/xen/common/inflate.c
>> @@ -244,7 +244,7 @@ static void *INIT malloc(int size)
>>
>> if (size < 0)
>> error("Malloc error");
>> - if (!malloc_ptr)
>> + if ((!malloc_ptr) || (!malloc_count))
>> malloc_ptr = free_mem_ptr;
>>
>
> IMHO, this is a bit risky to assume that malloc_count will always be 0
> after each gunzip.
>
> Instead I think, it would be better if we re-initialize the allocator
> every time.
I agree.
> How about the following (untested):
>
> commit e1cd2d85234c8d0aa62ad32c824a5568a57be930 (HEAD -> dev)
> Author: Julien Grall <jgrall@amazon.com>
> Date: Wed Mar 3 19:27:56 2021 +0000
>
> xen/gunzip: Allow perform_gunzip() to be called multiple times
>
> Currently perform_gunzip() can only be called once because the the
> internal allocator is not fully re-initialized.
>
> This works fine if you are only booting dom0. But this will break when
> booting multiple using the dom0less that uses compressed kernel images.
>
> This can be resolved by re-initializing malloc_ptr and malloc_count
> every time perform_gunzip() is called.
>
> Note the latter is only re-initialized for hardening purpose as
> there is
> no guarantee that every malloc() are followed by free() (It should in
> theory!).
>
> Take the opportunity to check the return of alloc_heap_pages() to
> return
> an error rather than dereferencing a NULL pointer later on failure.
>
> Reported-by: Charles Chiou <cchiou@ambarella.com>
> Signed-off-by: Julien Grall <jgrall@amazon.com>
>
> ---
>
> This patch is candidate for Xen 4.15. Without this patch, it will
> not be
> possible to boot multiple domain using dom0less when they are using
> compressed kernel images.
Other decompression methods are unaffected?
> --- a/xen/common/gunzip.c
> +++ b/xen/common/gunzip.c
> @@ -114,7 +114,11 @@ __init int perform_gunzip(char *output, char
> *image, unsigned long image_len)
> window = (unsigned char *)output;
>
> free_mem_ptr = (unsigned long)alloc_xenheap_pages(HEAPORDER, 0);
> + if ( !free_mem_ptr )
> + return -ENOMEM;
> +
> free_mem_end_ptr = free_mem_ptr + (PAGE_SIZE << HEAPORDER);
> + init_allocator();
>
> inbuf = (unsigned char *)image;
> insize = image_len;
> diff --git a/xen/common/inflate.c b/xen/common/inflate.c
> index f99c985d6135..d8c28a3e9593 100644
> --- a/xen/common/inflate.c
> +++ b/xen/common/inflate.c
> @@ -238,6 +238,12 @@ STATIC const ush mask_bits[] = {
> static unsigned long INITDATA malloc_ptr;
> static int INITDATA malloc_count;
>
> +static void init_allocator(void)
Please add INIT here. (I wouldn't mind if you used __init instead,
as there's going to be file-wide replacement after 4.15 anyway,
but of course this would render things inconsistent until then.)
Jan
> +{
> + malloc_ptr = free_mem_ptr;
> + malloc_count = 0;
> +}
> +
> static void *INIT malloc(int size)
> {
> void *p;
>
> Best regards,
>
next prev parent reply other threads:[~2021-03-04 8:35 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <c1b3f92388c34788b76193b70c150521@ambarella.com>
2021-03-03 19:36 ` dom0less boot two compressed kernel images out-of-memory work-around Julien Grall
2021-03-04 8:34 ` Jan Beulich [this message]
2021-03-04 10:28 ` Julien Grall
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