Re: [PATCH 03/19] target/ppc: add exclusive user write function for PMU regs

[Richard Henderson]

On 8/9/21 5:29 PM, David Gibson wrote:
> >       ctx->spr_cb = env->spr_cb;
> > +    ctx->spr = env->spr;
>
> Eep... with that one line you're copying 8kiB of data into the context
> structure.  That sounds undesirable.. especially since it look like
> you only check 8 bytes of it.
>
> Plus.. TBH, I'm a bit fuzzy on how the disascontext stuff works, but
> I'm not sure copying the stuff here is correct.

It isn't.

> I think instead you need to actually generate the instructions to read
> from MMCR0 and conditionally generate an exception if the permission
> bit isn't set.

Or copy exactly the bits you need from MMCR0 for the permission check into env->hflags, so 
that you can later read them from ctx->flags.  Bearing in mind that hflags has only 32 
bits, 19 of them are currently in use.


r~