Re: [Qemu-ppc] [RFC PATCH 05/17] KVM: PPC: booke: Extend MAS2 EPN mask for 64-bit

[Alexander Graf <agraf@suse.de>]

On 05.07.2012, at 13:14, Caraman Mihai Claudiu-B02008 wrote:

> 
> 
>> -----Original Message-----
>> From: Alexander Graf [mailto:agraf@suse.de]
>> Sent: Wednesday, July 04, 2012 4:50 PM
>> To: Caraman Mihai Claudiu-B02008
>> Cc: kvm-ppc@vger.kernel.org; kvm@vger.kernel.org; linuxppc-
>> dev@lists.ozlabs.org; qemu-ppc@nongnu.org
>> Subject: Re: [Qemu-ppc] [RFC PATCH 05/17] KVM: PPC: booke: Extend MAS2
>> EPN mask for 64-bit
>> 
>> 
>> On 25.06.2012, at 14:26, Mihai Caraman wrote:
>> 
>>> Extend MAS2 EPN mask for 64-bit hosts, to retain most significant bits.
>>> Change get tlb eaddr to use this mask.
>> 
>> Please see section 6.11.4.8 in the PowerISA 2.06b:
>> 
>> MMU behavior is largely unaffected by whether the thread is in 32-bit
>> computation mode (MSRCM=0) or 64- bit computation mode (MSRCM=1). The
>> only differ- ences occur in the EPN field of the TLB entry and the EPN
>> field of MAS2. The differences are summarized here.
>> 
>> 	*  Executing a tlbwe instruction in 32-bit mode will set bits 0:31
>> of the TLB EPN field to zero unless MAS0ATSEL is set, in which case those
>> bits are not written to zero.
>> 	*  In 32-bit implementations, MAS2U can be used to read or write
>> EPN0:31 of MAS2.
>> 
>> So if MSR.CM is not set tlbwe should mask the upper 32 bits out - which
>> can happen regardless of CONFIG_64BIT.
> 
> MAS2_EPN reflects EPN field of MAS2 aka bits 0:51 (for MAV = 1.0) according
> to section 6.10.3.10 in the PowerISA 2.06b.
> 
> MAS2_EPN is not used in tlbwe execution emulation, we have MAS2_VAL define
> for this case.

So tlbe->mas2 is guaranteed to have the upper bits be 0 when MSR.CM=0?

> 
>> Also, we need to implement MAS2U, to potentially make the upper 32bits of
>> MAS2 available, right? But that one isn't as important as the first bit.
> 
> MAS2U is guest privileged why does it need special care?

Maybe it's mapped to the upper bits of GMAS2 automatically?

> Freescale core Manuals and EREF does not mention MAS2U so I think I our case
> it is not implemented.

Please check with a simple mfspr() test on real hw to see if it really isn't implemented.


Alex