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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 1/5] xen/arm: optee: impose limit on shared buffer size
Hi Julien, Julien Grall writes: > Hi, > > On 9/12/19 8:45 PM, Volodymyr Babchuk wrote: >> >> Hi Julien, >> >> Julien Grall writes: >> >>> Hi Volodymyr, >>> >>> On 9/11/19 7:48 PM, Volodymyr Babchuk wrote: >>>> >>>> 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) I have missed that earlier. But 512 pages is 2MB, actually. >>>>> 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. >>> >>> Could we potentially reduce to let say 512KB (or maybe lower) if xtest >>> only allocate 32KB? >> Potentially - yes. But only to 512KB if we want to be compatible with >> the Global Platform specification. Why are you asking, though? > > Does the Global Platform specification limit to 512KB? Or is it a minimum? GP Spec says, that platform should allow *at lest* 512KB. Upper limit is not set. > Because, the smaller the buffer is, the less time it will take to > process in the worst case. Also, if we can have a reason for the size > (you seem to suggest the spec define a size...) then it is much better > than a random value. I have no strong arguments here, but I want to allow the biggest size possible. It seems, that 512 pages is the accepted limit in hypervisor code (at least, in p2m.c), so I chose this value. -- Volodymyr Babchuk at EPAM _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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