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SubjectRe: [RFC v2 00/12] powerpc: Memory Protection Keys
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On 06/20/2017 10:40 AM, Balbir Singh wrote:
> On Fri, 2017-06-16 at 20:52 -0700, Ram Pai wrote:
>> Memory protection keys enable applications to protect its
>> address space from inadvertent access or corruption from
>> itself.
>
> I presume by itself you mean protection between threads?

Between threads due to race conditions or from the same thread
because of programming error.

>
>>
>> The overall idea:
>>
>> A process allocates a key and associates it with
>> a address range within its address space.
>
> OK, so this is per VMA?

Yeah but the same key can be given to multiple VMAs. Any
change will effect every VMA who got tagged by it.

>
>> The process than can dynamically set read/write
>> permissions on the key without involving the
>> kernel.
>
> This bit is not clear, how can the key be set without
> involving the kernel? I presume you mean the key is set

With pkey_mprotect() system call, all the effected PTEs get
tagged for once. Switching the permission happens just by
writing into the register on the fly.

> in the PTE's and the access protection values can be
> set without involving the kernel?

PTE setting happens once, access protection values can be
changed on the fly through register.

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