Re: [PATCH 9/9] xen/arm64: Remove READ/WRITE_SYSREG32 helper macros

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi Jilien,

On 21.04.2021 21:16, Julien Grall wrote:
> Hi Michal,
> 
> On 20/04/2021 08:08, Michal Orzel wrote:
>> AArch64 system registers are 64bit whereas AArch32 ones
>> are 32bit or 64bit. MSR/MRS are expecting 64bit values thus
>> we should get rid of helpers READ/WRITE_SYSREG32
>> in favour of using READ/WRITE_SYSREG.
>> We should also use register_t type when reading sysregs
>> which can correspond to uint64_t or uint32_t.
>> Even though many AArch64 sysregs have upper 32bit reserved
>> it does not mean that they can't be widen in the future.
> 
> As a general comment, all your commit message contains information about the 
> goal (which is great). But they don't go much in details about the actual 
> changes. I have tried to point out where I think those details would be 
> helpful.
> 
>>
>> As there are no other places in the code using READ/WRITE_SYSREG32,
>> remove the helper macros.
>>
>> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
>> ---
>>   xen/arch/arm/vcpreg.c               | 16 ++++++++++++++++
>>   xen/include/asm-arm/arm64/sysregs.h |  5 -----
>>   2 files changed, 16 insertions(+), 5 deletions(-)
>>
>> diff --git a/xen/arch/arm/vcpreg.c b/xen/arch/arm/vcpreg.c
>> index c7f516ee0a..6cb7f3108c 100644
>> --- a/xen/arch/arm/vcpreg.c
>> +++ b/xen/arch/arm/vcpreg.c
>> @@ -48,6 +48,7 @@
>>    */
>>     /* The name is passed from the upper macro to workaround macro 
>> expansion. */
>> +#ifdef CONFIG_ARM_32
>>   #define TVM_REG(sz, func, reg...)                                          
>>  \
>>   static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, bool read)   
>>  \
>>   {                                                                          
>>  \
>> @@ -61,6 +62,21 @@ static bool func(struct cpu_user_regs *regs, uint##sz##_t 
>> *r, bool read)    \
>>                                                                              
>>  \
>>       return true;                                                           
>>  \
>>   }
>> +#else /* CONFIG_ARM_64 */
>> +#define TVM_REG(sz, func, reg...)                                           
>> \
>> +static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, bool read)    
>> \
>> +{                                                                           
>> \
>> +    struct vcpu *v = current;                                               
>> \
>> +    bool cache_enabled = vcpu_has_cache_enabled(v);                         
>> \
>> +                                                                            
>> \
>> +    GUEST_BUG_ON(read);                                                     
>> \
>> +    WRITE_SYSREG(*r, reg);                                                  
>> \
>> +                                                                            
>> \
>> +    p2m_toggle_cache(v, cache_enabled);                                     
>> \
>> +                                                                            
>> \
>> +    return true;                                                            
>> \
>> +}
>> +#endif
> 
> It would be nice if this change can be explained in the commit message. 
> However, I think we can avoid the duplication by aliasing TVM_REG32() to 
> TVM_REG64() on Arm64.
> 
Unfortunately we cannot. This is the only working solution for now.
If we do the alias we will get many errors due to incompatbile pointer type in 
vreg_emulate_*.
Without a proper change in this functions we can't do that.
I will modify it once I start working on vreg_emulate topic but it requires 
more investigation.

For now I'd suggest to keep it as it is + explain the change in the commit.
I will push v2 soon.
>>     #define TVM_REG32(regname, xreg) TVM_REG(32, vreg_emulate_##regname, 
>> xreg)
>>   #define TVM_REG64(regname, xreg) TVM_REG(64, vreg_emulate_##regname, xreg)
>> diff --git a/xen/include/asm-arm/arm64/sysregs.h 
>> b/xen/include/asm-arm/arm64/sysregs.h
>> index 077fd95fb7..83a1157ac4 100644
>> --- a/xen/include/asm-arm/arm64/sysregs.h
>> +++ b/xen/include/asm-arm/arm64/sysregs.h
>> @@ -86,11 +86,6 @@
>>   #endif
>>     /* Access to system registers */
>> -
>> -#define READ_SYSREG32(name) ((uint32_t)READ_SYSREG64(name))
>> -
>> -#define WRITE_SYSREG32(v, name) WRITE_SYSREG64((uint64_t)v, name)
>> -
>>   #define WRITE_SYSREG64(v, name) do {                    \
>>       uint64_t _r = v;                                    \
>>       asm volatile("msr "__stringify(name)", %0" : : "r" (_r));       \
>>
> 
> Cheers,
> 
Cheers,
Michal