Re: [PATCH Part2 RFC v4 25/40] KVM: SVM: Reclaim the guest pages when SEV-SNP VM terminates

[Sean Christopherson]

On Mon, Jul 19, 2021, Sean Christopherson wrote:
> On Mon, Jul 19, 2021, Brijesh Singh wrote:
> > 
> > On 7/19/21 12:18 PM, Sean Christopherson wrote:
> > > > 
> > > > Okay, I will add helper to make things easier. One case where we will
> > > > need to directly call the rmpupdate() is during the LAUNCH_UPDATE
> > > > command. In that case the page is private and its immutable bit is also
> > > > set. This is because the firmware makes change to the page, and we are
> > > > required to set the immutable bit before the call.
> > > 
> > > Or do "int rmp_make_firmware(u64 pfn, bool immutable)"?
> > 
> > That's not what we need.
> > 
> > We need 'rmp_make_private() + immutable' all in one RMPUPDATE.  Here is the
> > snippet from SNP_LAUNCH_UPDATE.
> 
> Ah, not firmwrare, gotcha.  But we can still use a helper, e.g. an inner
> double-underscore helper, __rmp_make_private().

Hmm, looking at it again, I think I also got confused by the comment for the VMSA
page:

	/* Transition the VMSA page to a firmware state. */
 	e.assigned = 1;
	e.immutable = 1;
	e.asid = sev->asid;
	e.gpa = -1;
	e.pagesize = RMP_PG_SIZE_4K;

Unlike __snp_alloc_firmware_pages() in the CCP code, the VMSA is associated with
the guest's ASID, just not a GPA.  I.e. the VMSA is more of a specialized guest
private page, as opposed to a dedicated firmware page.  I.e. a __rmp_make_private()
and/or rmp_make_private_immutable() definitely seems like a good idea.