From: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
To: Julien Grall <julien.grall@arm.com>
Cc: "tee-dev@lists.linaro.org" <tee-dev@lists.linaro.org>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Stefano Stabellini <sstabellini@kernel.org>,
Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [PATCH 1/5] xen/arm: optee: impose limit on shared buffer size
Date: Wed, 11 Sep 2019 18:48:39 +0000 [thread overview]
Message-ID: <87k1aefz3t.fsf@epam.com> (raw)
In-Reply-To: <45208af4-22b8-2870-f79d-a98960c4700d@arm.com>
Julien Grall writes:
> Hi Volodymyr,
>
> On 8/23/19 7:48 PM, Volodymyr Babchuk wrote:
>> We want to limit number of calls to lookup_and_pin_guest_ram_addr()
>> per one request. There are two ways to do this: either preempt
>> translate_noncontig() or to limit size of one shared buffer size.
>>
>> It is quite hard to preempt translate_noncontig(), because it is deep
>> nested. So we chose second option. We will allow 512 pages per one
>> shared buffer. This does not interfere with GP standard, as it
>> requires that size limit for shared buffer should be at lest 512kB.
>
> Do you mean "least" instead of "lest"?
Yes
> If so, why 512 pages (i.e 1MB)
> is plenty enough for most of the use cases? What does "xtest" consist
> on?
Bigger buffer xtest tries to allocate is mere 32KB. I believe that 1MB
is enough for the most cases, because OP-TEE itself have a very limited
resources. But this value is chosen arbitrary.
>
>> Also, with this limitation OP-TEE still passes own "xtest" test suite,
>> so this is okay for now.
>>
>> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
>> ---
>> xen/arch/arm/tee/optee.c | 30 ++++++++++++++++++------------
>> 1 file changed, 18 insertions(+), 12 deletions(-)
>>
>> diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
>> index ec5402e89b..f4fa8a7758 100644
>> --- a/xen/arch/arm/tee/optee.c
>> +++ b/xen/arch/arm/tee/optee.c
>> @@ -72,6 +72,17 @@
>> */
>> #define MAX_TOTAL_SMH_BUF_PG 16384
>> +/*
>> + * Arbitrary value that limits maximum shared buffer size. It is
>> + * merely coincidence that it equals to both default OP-TEE SHM buffer
>> + * size limit and to (1 << CONFIG_DOMU_MAX_ORDER). Please note that
>> + * this define limits number of pages. But user buffer can be not
>> + * aligned to a page boundary. So it is possible that user would not
>> + * be able to share exactly MAX_SHM_BUFFER_PG * PAGE_SIZE bytes with
>> + * OP-TEE.
>> + */
>> +#define MAX_SHM_BUFFER_PG 512
>> +
>> #define OPTEE_KNOWN_NSEC_CAPS OPTEE_SMC_NSEC_CAP_UNIPROCESSOR
>> #define OPTEE_KNOWN_SEC_CAPS (OPTEE_SMC_SEC_CAP_HAVE_RESERVED_SHM | \
>> OPTEE_SMC_SEC_CAP_UNREGISTERED_SHM | \
>> @@ -697,15 +708,17 @@ static int translate_noncontig(struct optee_domain *ctx,
>> size = ROUNDUP(param->u.tmem.size + offset, OPTEE_MSG_NONCONTIG_PAGE_SIZE);
>> pg_count = DIV_ROUND_UP(size,
>> OPTEE_MSG_NONCONTIG_PAGE_SIZE);
>> + if ( pg_count > MAX_SHM_BUFFER_PG )
>> + return -ENOMEM;
>> +
>> order = get_order_from_bytes(get_pages_list_size(pg_count));
>> /*
>> - * In the worst case we will want to allocate 33 pages, which is
>> - * MAX_TOTAL_SMH_BUF_PG/511 rounded up. This gives order 6 or at
>> - * most 64 pages allocated. This buffer will be freed right after
>> - * the end of the call and there can be no more than
>> + * In the worst case we will want to allocate 2 pages, which is
>> + * MAX_SHM_BUFFER_PG/511 rounded up. This buffer will be freed
>> + * right after the end of the call and there can be no more than
>> * max_optee_threads calls simultaneously. So in the worst case
>> - * guest can trick us to allocate 64 * max_optee_threads pages in
>> + * guest can trick us to allocate 2 * max_optee_threads pages in
>> * total.
>> */
>> xen_pgs = alloc_domheap_pages(current->domain, order, 0);
>> @@ -747,13 +760,6 @@ static int translate_noncontig(struct optee_domain *ctx,
>> xen_data = __map_domain_page(xen_pgs);
>> }
>> - /*
>> - * TODO: That function can pin up to 64MB of guest memory by
>> - * calling lookup_and_pin_guest_ram_addr() 16384 times
>> - * (assuming that PAGE_SIZE equals to 4096).
>> - * This should be addressed before declaring OP-TEE security
>> - * supported.
>> - */
>> BUILD_BUG_ON(PAGE_SIZE != 4096);
>
> Without the comment, the BUILD_BUG_ON() looks random. So either you
> want to have a different version of the comment or you want to move
> the BUILD_BUG_ON() to somewhere else.
It is still before get_domain_ram_page() call. But for clarity I can add
comment like "Only 4k pages are supported right now".
>> page = get_domain_ram_page(gaddr_to_gfn(guest_data->pages_list[idx]));
>> if ( !page )
>>
>
> Cheers,
--
Volodymyr Babchuk at EPAM
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next prev parent reply other threads:[~2019-09-11 18:49 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-23 18:48 [Xen-devel] [PATCH 0/5] arch/arm: optee: fix TODOs and remove "experimental" status Volodymyr Babchuk
2019-08-23 18:48 ` [Xen-devel] [PATCH 1/5] xen/arm: optee: impose limit on shared buffer size Volodymyr Babchuk
2019-09-09 22:11 ` Julien Grall
2019-09-11 18:48 ` Volodymyr Babchuk [this message]
2019-09-12 19:32 ` Julien Grall
2019-09-12 19:45 ` Volodymyr Babchuk
2019-09-12 19:51 ` Julien Grall
2019-09-16 15:26 ` Volodymyr Babchuk
2019-09-17 10:49 ` Julien Grall
2019-09-17 12:28 ` Volodymyr Babchuk
2019-09-17 18:46 ` Julien Grall
2019-08-23 18:48 ` [Xen-devel] [PATCH 2/5] xen/arm: optee: check for preemption while freeing shared buffers Volodymyr Babchuk
2019-09-09 22:19 ` Julien Grall
2019-09-11 18:53 ` Volodymyr Babchuk
2019-09-12 19:39 ` Julien Grall
2019-09-12 19:47 ` Volodymyr Babchuk
2019-08-23 18:48 ` [Xen-devel] [PATCH 3/5] xen/arm: optee: limit number of " Volodymyr Babchuk
2019-08-23 18:48 ` [Xen-devel] [PATCH 4/5] xen/arm: optee: handle share buffer translation error Volodymyr Babchuk
2019-09-10 11:17 ` Julien Grall
2019-09-11 18:32 ` Volodymyr Babchuk
2019-09-12 18:55 ` Julien Grall
2019-08-23 18:48 ` [Xen-devel] [PATCH 5/5] xen/arm: optee: remove experimental status Volodymyr Babchuk
2019-08-23 19:05 ` Julien Grall
2019-08-23 19:20 ` Volodymyr Babchuk
2019-09-09 21:31 ` Julien Grall
2019-09-11 18:41 ` Volodymyr Babchuk
2019-09-12 19:00 ` Julien Grall
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