lkml.org 
[lkml]   [2021]   [Jan]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v1 4/4] s390/kvm: VSIE: correctly handle MVPG when in VSIE
    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
    >
    > 1. "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;
    > > }
    > > return rc;
    > > }
    > >
    >
    >

    \
     
     \ /
      Last update: 2021-01-04 16:27    [W:3.005 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site