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Re: [Xen-devel] [PATCH] xen/arm: Restricted access to IFSR32_EL2 and FPEXC32_EL2

Hi Julien,

On Tue, May 27, 2014 at 4:51 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> Hi Vijaya,
> On 05/27/2014 11:37 AM, vijay.kilari@xxxxxxxxx wrote:
>> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
>> Some platforms does not support aarch32 mode. So access only if
>> platform supports it. Accessing these registers will
>> raise exception
>> Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
>> ---
>>  xen/arch/arm/arm64/vfp.c |    6 ++++--
>>  xen/arch/arm/traps.c     |    7 +++++--
>>  2 files changed, 9 insertions(+), 4 deletions(-)
>> diff --git a/xen/arch/arm/arm64/vfp.c b/xen/arch/arm/arm64/vfp.c
>> index 3cd2b1b..c550a68 100644
>> --- a/xen/arch/arm/arm64/vfp.c
>> +++ b/xen/arch/arm/arm64/vfp.c
>> @@ -28,7 +28,8 @@ void vfp_save_state(struct vcpu *v)
>>      v->arch.vfp.fpsr = READ_SYSREG32(FPSR);
>>      v->arch.vfp.fpcr = READ_SYSREG32(FPCR);
>> -    v->arch.vfp.fpexc32_el2 = READ_SYSREG32(FPEXC32_EL2);
>> +    if ( cpu_has_el2_32 )
> You should use is_32bit_domain here. If your platform doesn't support
> aarch32 mode, then we should not create 32bit domain.

I agree as per ARM Spec, it says if aarch32 mode is supported and so if
the domain is 32-bit then only these registers are allowed

"The following registers are defined to allow access from AArch64 state to
registers that are only used in AArch32 state

SDER32_EL3    If EL1 cannot use AArch32, this register is UNDEFINED.
DACR32_EL2    If EL1 cannot use AArch32, this register is UNDEFINED.
IFSR32_EL2     If EL1 cannot use AArch32, this register is UNDEFINED.
FPEXC32_EL2  If EL1 cannot use AArch32, this register is UNDEFINED."

> I think you will have to deny somewhere the domain creation in this case.

Here I found that for dom0 a check is made in construct_dom0() where
domain type is being set to allow only 64-bit domains if platform supports
only aarch64 bit mode.

However for domU, arch.type is being set using  hypercall
"XEN_DOMCTL_set_address_size:" defined in arch/arm/arm64/domctl.c in

So questions are :
1) Is this the hypercall where domain type is set?. If so, can we
return error for this
    hypercall if domU type is not supported by Xen?
2) Can xl tool allow to load domU that platform supports?. May be it require
    hardware info here which may not be right way to do.


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