Re: [RFC v2 03/17] x86/apic: Populate .read()/.write() callbacks of Secure AVIC driver

[Neeraj Upadhyay]

On 3/21/2025 7:08 PM, Thomas Gleixner wrote:
> On Wed, Feb 26 2025 at 14:35, Neeraj Upadhyay wrote:
> 
>> +static inline u32 get_reg(char *page, int reg)
>> +{
>> +	return READ_ONCE(*((u32 *)(page + reg)));
> 
> This type casting is disgusting. First you cast the void pointer of the
> per CPU backing page implicitely into a signed character pointer and
> then cast that to a u32 pointer. Seriously?
> 
> struct apic_page {
> 	union {
> 		u32	regs[NR_APIC_REGS];
>                 u8	bytes[PAGE_SIZE];
> 	};
> };                
> 
> and the per CPU allocation of apic_page makes this:
> 
> static __always_inline u32 get_reg(unsigned int offset)
> {
>         return READ_ONCE(this_cpu_ptr(apic_page)->regs[offset >> 2]));
> }
> 
> which avoids the whole pointer indirection of your backing page construct.
> 

Thanks for suggesting this!

- Neeraj

> Thanks,
> 
>         tglx