Re: [RFC PATCH 0/5] madvise MADV_DOEXEC

Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-08-16T00:28:27Z

Hi David,

在 2021/8/15 4:07, David Laight 写道:
> ...
>>>>> Let me describe my use case more clearly (just ignore if you're not
>>>>> interested in it):
>>>>>
>>>>> 1. Prog A mmap() 4GB memory (anon or file-mapping), suppose the
>>>>> allocated VA range is [0x40000000,0x140000000)
>>>>>
>>>>> 2. Prog A specifies [0x48000000,0x50000000) and
>>>>> [0x80000000,0x100000000) will be shared by its child.
>>>>>
>>>>> 3. Prog A fork() Prog B and then Prog B exec() a new ELF binary.
>>>>>
>>>>> 4. Prog B notice the shared ranges (e.g. by input parameters or
>>>>> ...)
>>>>> and remap them to a continuous VA range.
>
> Remapping to contiguous VA is going to be difficult in the
> general case for (IIRC) VIVT caches.
> The required cache coherence may only be attainable by
> using uncached mappings.
>

The Prog B uses mremap() syscall to remapping the shared ranges to other places,
this is a common case for mremap in userspace.
The cache coherence should already be processed in mremap core logic, otherwise
there's maybe something wrong in mremap().

> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>