Re: [RFC v7 09/25] powerpc: store and restore the pkey state across context switches

[Michael Ellerman <mpe@ellerman.id.au>]

Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> writes:

> Ram Pai <linuxram@us.ibm.com> writes:
>> --- a/arch/powerpc/kernel/process.c
>> +++ b/arch/powerpc/kernel/process.c
>> @@ -42,6 +42,7 @@
>>  #include <linux/hw_breakpoint.h>
>>  #include <linux/uaccess.h>
>>  #include <linux/elf-randomize.h>
>> +#include <linux/pkeys.h>
>>
>>  #include <asm/pgtable.h>
>>  #include <asm/io.h>
>> @@ -1096,6 +1097,13 @@ static inline void save_sprs(struct thread_struct *t)
>>  		t->tar = mfspr(SPRN_TAR);
>>  	}
>>  #endif
>> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>> +	if (arch_pkeys_enabled()) {
>> +		t->amr = mfspr(SPRN_AMR);
>> +		t->iamr = mfspr(SPRN_IAMR);
>> +		t->uamor = mfspr(SPRN_UAMOR);
>> +	}
>> +#endif
>>  }
>
> Is it worth having a flag in thread_struct saying whether it has every
> called pkey_alloc and only do the mfsprs if it did?

Yes, in fact there's a programming note in the UAMOR section of the arch
that says exactly that.

On the write side you have to be a bit more careful. You have to make
sure you set the UAMOR to 0 when you're switching from a process that
has used keys to one that isn't.

cheers