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

Venu Busireddy
2022-01-06T17:41:51Z

On 2022-01-05 15:39:22 -0600, Brijesh Singh wrote:
>
>
> 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.

Looking forward to see your final comments explaining this. I can't
still follow why, when PVALIDATE needs the virtual address, we are doing
a __pa() on the vaddr.

Venu