Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section shared in RMP table

[Brijesh Singh]

On 1/5/22 2:27 PM, Dave Hansen wrote:
> On 1/5/22 11:52, Brijesh Singh wrote:
> > > >           for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
> > > > +            /*
> > > > +             * When SEV-SNP is active then transition the page to 
> > > > shared in the RMP
> > > > +             * table so that it is consistent with the page table 
> > > > attribute change.
> > > > +             */
> > > > +            early_snp_set_memory_shared(__pa(vaddr), __pa(vaddr), 
> > > > PTRS_PER_PMD);
> > >
> > > Shouldn't the first argument be vaddr as below?
> >
> > Nope, sme_postprocess_startup() is called while we are fixing the 
> > initial page table and running with identity mapping (so va == pa).
>
> I'm not sure I've ever seen a line of code that wanted a comment so badly.

The early_snp_set_memory_shared() call the PVALIDATE instruction to 
clear the validated bit from the BSS region. The PVALIDATE instruction 
needs a virtual address, so we need to use the identity mapped virtual 
address so that PVALIDATE can clear the validated bit. I will add more 
comments to clarify it.

-Brijesh