Re: [RFC PATCH 2/3] nSVM: introduce smv->nested.save to cache save area fields

[Paolo Bonzini]

On 12/09/21 12:39, Maxim Levitsky wrote:
> On Fri, 2021-09-03 at 12:20 +0200, Emanuele Giuseppe Esposito wrote:
> > This is useful in next patch, to avoid having temporary
> > copies of vmcb12 registers and passing them manually.
>
> This is NOT what I had in mind, but I do like that idea very much,
> IMHO this is much better than what I had in mind!
>
> The only thing that I would change is that I woudn't reuse 'struct vmcb_save_area'
> for the copy, as this both wastes space (minor issue),
> and introduces a chance of someone later using non copied
> fields from it (can cause a bug later on).
>
> I would just define a new struct for that (but keep same names
> for readability)
>
> Maybe something like 'struct vmcb_save_area_cached'?

I agree, I like this too.  However, it needs a comment that this new 
struct is not kept up-to-date, and is only valid until enter_svm_guest_mode.

I might even propose a

#ifdef CONFIG_DEBUG_KERNEL
	memset(&svm->nested.save, 0xaf, sizeof(svm->nested.save));
#endif

but there are no uses of CONFIG_DEBUG_KERNEL in all of Linux so it's 
probably not the way one should use that symbol.  Can anybody think of a 
similar alternative?  Or should the memset simply be unconditional?

Paolo