[PATCH 2/2] arm64: kvm: upgrade csselr and ccsidr to 64-bit values

[Sudeep Holla]

On 24/01/17 10:30, Christoffer Dall wrote:
> On Tue, Jan 24, 2017 at 10:15:38AM +0000, Sudeep Holla wrote:
>>
>>
>> On 23/01/17 21:08, Christoffer Dall wrote:
>>> On Fri, Jan 20, 2017 at 10:50:10AM +0000, Sudeep Holla wrote:
>>>> csselr and ccsidr are treated as 64-bit values already elsewhere in the
>>>> kernel. It also aligns well with the architecture extensions that allow
>>>> 64-bit format for ccsidr.
>>>>
>>>> This patch upgrades the existing accesses to csselr and ccsidr from
>>>> 32-bit to 64-bit in preparation to add support to those extensions.
>>>>
>>>> Cc: Christoffer Dall <christoffer.dall at linaro.org>
>>>> Cc: Marc Zyngier <marc.zyngier at arm.com>
>>>> Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
>>>> ---
>>>>  arch/arm64/kvm/sys_regs.c | 18 +++++++++---------
>>>>  1 file changed, 9 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>>> index 5dca1f10340f..a3559a8a2b0c 100644
>>>> --- a/arch/arm64/kvm/sys_regs.c
>>>> +++ b/arch/arm64/kvm/sys_regs.c
>>
>> [..]
>>
>>>> @@ -2004,8 +2004,8 @@ static int demux_c15_get(u64 id, void __user *uaddr)
>>>>  
>>>>  static int demux_c15_set(u64 id, void __user *uaddr)
>>>>  {
>>>> -	u32 val, newval;
>>>> -	u32 __user *uval = uaddr;
>>>> +	u64 val, newval;
>>>> +	u64 __user *uval = uaddr;
>>>
>>> Doesn't converting these uval pointers to u64 cause us to break the ABI
>>> as we'll now be reading/writing 64-bit values to userspace with the
>>> get_user and put_user following the declarations?
>>>
>>
>> Yes, I too have similar concern. IIUC it is always read via kvm_one_reg
>> structure. I could not find any specific user for this register to cross
>> check.
>>
> 
> Not sure it matters which interface we get the userspace pointer from?
> 

Agreed.

> This patch is definitely changing the write from a 32-bit write to a
> 64-bit write and there's a specific check prior to the put_user() call
> which checks that userspace intended a 32-bit value and presumably
> provided a 32-bit pointer.
> 

I see you point, I missed to see that check(just to be sure KVM_REG_SIZE
check right ?).

> So I think the only way to return 64-bit AArch32 system register values
> to userspace (if that is the intention) is to define a new ID for 64-bit
> CCSIDR registers and handle them separately.
> 

I will add KVM_REG_ARM_DEMUX_ID_CCSIDR_64B or something similar.
Thanks for the review.

-- 
Regards,
Sudeep