On Fri, Jul 16, 2021, Brijesh Singh wrote:

On 7/16/21 2:19 PM, Sean Christopherson wrote:

quoted

On Wed, Jul 07, 2021, Brijesh Singh wrote:
Another option would be to drop the kvm_x86_ops hooks entirely and call
snp_lookup_page_in_rmptable() directly from MMU code.  That would require tracking
that a VM is SNP-enabled in arch code, but I'm pretty sure info has already bled
into common KVM in one form or another.

I would prefer this as it eliminates some of the other unnecessary call
sites. Unfortunately, currently there is no generic way to know if its
an SEV guest (outside the svm/*).  So far there was no need as such but
with SNP having such information would help. Should we extend the
'struct kvm' to include a new field that can be used to determine the
guest type. Something like

enum {

   GUEST_TYPE_SEV,

   GUEST_TYPE_SEV_ES,

   GUEST_TYPE_SEV_SNP,

};

struct kvm {

   ...

  u64 enc_type;

};

bool kvm_guest_enc_type(struct kvm *kvm, enum type); {

    return !!kvm->enc_type & type;

}

The mmu.c can then call kvm_guest_enc_type() to check if its SNP guest
and use the SNP lookup directly to determine the pagesize.

The other option is to use vm_type, which TDX is already planning on leveraging.
Paolo raised the question of whether or not the TDX type could be reused for SNP.
We should definitely sort that out before merging either series.  I'm personally
in favor of separating TDX and SNP, it seems inevitable that common code will
want to differentiate between the two.

https://lkml.kernel.org/r/8eb87cd52a89d957af03f93a9ece5634426a7757.1625186503.git.isaku.yamahata@intel.com

quoted

As the APM is currently worded, this is wrong, and the whole "tdp_max_page_level"
name is wrong.  As noted above, the Page-Size bullet points states that 2mb/1gb
pages in the NPT _must_ have RMP.page_size=1, and 4kb pages in the NPT _must_
have RMP.page_size=0.  That means that the RMP adjustment is not a constraint,
it's an exact requirement.  Specifically, if the RMP is a 2mb page then KVM must
install a 2mb (or 1gb) page.  Maybe it works because KVM will PSMASH the RMP
after installing a bogus 4kb NPT and taking an RMP violation, but that's a very
convoluted and sub-optimal solution.

This is why I was passing the preferred max_level in the pre-fault
handle then later query the npt level; use the npt level in the RMP to
make sure they are in sync.

There is yet another reason why we can't avoid the PSMASH after doing
everything to ensure that NPT and RMP are in sync. e.g if NPT and RMP
are programmed with 2mb size but the guest tries to PVALIDATE the page
as a 4k. In that case, we will see #NPF with page size mismatch and have
to perform psmash.

Boo, there's no way to communicate to the guest that it's doing PVALIDATE wrong
is there?