Re: [RFC PATCH v1 13/15] x86/msr: Use the alternatives mechanism to read MSR

[Xin Li <xin@xxxxxxxxx>]

On 4/14/2025 10:13 AM, Francesco Lavra wrote:
> This works only if this function has been called directly (e.g. via
> `call asm_xen_write_msr`), but doesn't work with alternative call types
> (like indirect calls). Not sure why one might want to use an indirect
> call to invoke asm_xen_write_msr, but this creates a hidden coupling
> between caller and callee.
> I don't have a suggestion on how to get rid of this coupling, other
> than setting ipdelta in _ASM_EXTABLE_FUNC_REWIND() to 0 and adjusting
> the _ASM_EXTABLE_TYPE entries at the call sites to consider the
> instruction that follows the function call (instead of the call
> instruction) as the faulting instruction (which seems pretty ugly, at
> least because what follows the function call could be an instruction
> that might itself fault). But you may want to make this caveat explicit
> in the comment.
Good idea, will state that in the comment.