Re: [PATCH v6 2/9] xen/riscv: use {read,write}{b,w,l,q}_cpu() to define {read,write}_atomic()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 04/09/2024 11:27 am, oleksii.kurochko@xxxxxxxxx wrote:
> On Tue, 2024-09-03 at 15:21 +0100, Andrew Cooper wrote:
>> On 02/09/2024 6:01 pm, Oleksii Kurochko wrote:
>>> diff --git a/xen/arch/riscv/include/asm/atomic.h
>>> b/xen/arch/riscv/include/asm/atomic.h
>>> index 31b91a79c8..3c6bd86406 100644
>>> --- a/xen/arch/riscv/include/asm/atomic.h
>>> +++ b/xen/arch/riscv/include/asm/atomic.h
>>> @@ -31,21 +31,17 @@
>>>  
>>>  void __bad_atomic_size(void);
>>>  
>>> -/*
>>> - * Legacy from Linux kernel. For some reason they wanted to have
>>> ordered
>>> - * read/write access. Thereby read* is used instead of read*_cpu()
>>> - */
>>>  static always_inline void read_atomic_size(const volatile void *p,
>>>                                             void *res,
>>>                                             unsigned int size)
>>>  {
>>>      switch ( size )
>>>      {
>>> -    case 1: *(uint8_t *)res = readb(p); break;
>>> -    case 2: *(uint16_t *)res = readw(p); break;
>>> -    case 4: *(uint32_t *)res = readl(p); break;
>>> +    case 1: *(uint8_t *)res = readb_cpu(p); break;
>>> +    case 2: *(uint16_t *)res = readw_cpu(p); break;
>>> +    case 4: *(uint32_t *)res = readl_cpu(p); break;
>>>  #ifndef CONFIG_RISCV_32
>>> -    case 8: *(uint32_t *)res = readq(p); break;
>>> +    case 8: *(uint32_t *)res = readq_cpu(p); break;
>> This cast looks suspiciously like it's wrong already in staging...
> Thanks for noticing that, it should be really uint64_t. I'll update
> that in the next patch version.

This bug is in 4.19.

I know RISC-V is experimental, but this is the kind of thing that Jan
might consider for backporting.

Whether it gets backported or not, it wants to be in a standalone
bugfix, not as a part of "rewrite the accessors used".

~Andrew