On Sun, 20 Dec 2020 11:13:57 +0100 David Hildenbrand david@redhat.com wrote:
On 18.12.20 15:18, Claudio Imbrenda wrote:
Correctly handle the MVPG instruction when issued by a VSIE guest.
I remember that MVPG SIE documentation was completely crazy and full of corner cases. :)
you remember correctly
Looking at arch/s390/kvm/intercept.c:handle_mvpg_pei(), I can spot that
- "This interception can only happen for guests with DAT disabled
..." 2. KVM does not make use of any mvpg state inside the SCB.
Can this be observed with Linux guests?
a Linux guest will typically not run with DAT disabled
Can I get some information on what information is stored at [0xc0, 0xd) inside the SCB? I assume it's:
0xc0: guest physical address of source PTE 0xc8: guest physical address of target PTE
yes (plus 3 flags in the lower bits of each)
Also, which conditions have to be met such that we get a ICPT_PARTEXEC:
a) State of guest DAT (I assume off?) b) State of PTEs: What happens if there is no PTE (I assume we need two PTEs, otherwise no such intercept)? I assume we get an intercept if one of both PTEs is not present or the destination PTE is protected. Correct?
we get the intercept if the guest has DAT off, and at least one of the host PTEs is invalid (and I think if the destination is valid but protected)
So, when we (g1) get an intercept for g3, can we be sure 0xc0 and 0xc8 in the scb are both valid g1 addresses pointing at our PTE, and what do we know about these PTEs (one not present or destination protected)?
we only know that at least one of the following holds true: * source invalid * destination invalid * destination protected
there is a bit that tells us if the destination was protected (bit 62), but that does not exclude an invalid source
[...]
/*
- Run the vsie on a shadow scb and a shadow gmap, without any
further
- sanity checks, handling SIE faults.
@@ -1063,6 +1132,10 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) if ((scb_s->ipa & 0xf000) != 0xf000) scb_s->ipa += 0x1000; break;
- case ICPT_PARTEXEC:
if (scb_s->ipa == 0xb254)Old code hat "/* MVPG only */" - why is this condition now necessary?
old code was wrong ;)
rc = vsie_handle_mvpg(vcpu, vsie_page);break;}