Re: [Qemu-devel] [PATCH v2 1/2] ppc/pnv: Add model for Power8 PHB3 PCIe Host bridge

[Benjamin Herrenschmidt]

On Thu, 2018-07-26 at 11:03 +0200, Cédric Le Goater wrote:
> Ben,
> 
> I have found out recently that the QEMU PowerNV could hang while accessing
> the disk. 
> 
> The issue seems to be the phb3_msi_try_send() routine when called from 
> the resend() handler. The 'P' is ignored in that case but not the 'Q' 
> bit which means that no interrupt will be resent if P|Q are set. 

I'd have to remember how PQ works on P8 ... my gut feeling is that we
should resend if P=1 but I'm no 100% certain.

> See the log extract below  :
> 
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005000000fd eff pq=0 
> prio=5 server=8 ignore_p=0
>   PHB3(phb3_msi_set_p): MSI 0: setting P
>   PHB3(phb3_msi_set_p):  IVE readback: 0x2005010000fd
>   PHB3(phb3_msi_reject): MSI 0 rejected
>   PHB3(phb3_msi_resend): MSI resend...
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005010000fd eff pq=0 
> prio=5 server=8 ignore_p=1
>   PHB3(phb3_msi_set_p): MSI 0: setting P
>   PHB3(phb3_msi_set_p):  IVE readback: 0x2005010000fd
>   PHB3(phb3_msi_reject): MSI 0 rejected
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005010000fd eff pq=2 
> prio=5 server=8 ignore_p=0
>   PHB3(phb3_msi_set_q): MSI 0: setting Q
>   PHB3(phb3_msi_set_q):  IVE readback: 0x2005010100fd
>   PHB3(phb3_msi_resend): MSI resend...
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005010100fd eff pq=1 
> prio=5 server=8 ignore_p=1
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005010100fd eff pq=3 
> prio=5 server=8 ignore_p=0
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005010100fd eff pq=3 
> prio=5 server=8 ignore_p=0
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005010100fd eff pq=3 
> prio=5 server=8 ignore_p=0
>   PHB3(phb3_msi_try_send): MSI 0: try_send, ive=0x2005010100fd eff pq=3 
> prio=5 server=8 ignore_p=0
>   ... goes on and on ...
>   hangs
> 
> I have added the relevant code at the bottom of the email. 
> 
> 
> If the 'Q' bit is ignored also, the results are good with a SATA drive 
> or a SCSI drive using the megasas model. Do you think this is correct ?
> I would say so but I am still discovering that part.
> 
> I have no idea why it didn't show up before. May be because we mostly 
> used virtio-blk.
> 
> Thanks,
> 
> C. 
> 
> > +static void phb3_msi_try_send(Phb3MsiState *msi, int srcno, bool ignore_p)
> > +{
> > +    ICSState *ics = ICS_BASE(msi);
> > +    uint64_t ive;
> > +    uint64_t server, prio, pq, gen;
> > +
> > +    if (!phb3_msi_read_ive(msi->phb, srcno, &ive)) {
> > +        return;
> > +    }
> > +
> > +    server = GETFIELD(IODA2_IVT_SERVER, ive);
> > +    prio = GETFIELD(IODA2_IVT_PRIORITY, ive);
> > +    pq = GETFIELD(IODA2_IVT_Q, ive);
> > +    if (!ignore_p) {
> > +        pq |= GETFIELD(IODA2_IVT_P, ive) << 1;
> > +    }
> > +    gen = GETFIELD(IODA2_IVT_GEN, ive);
> > +
> > +    /*
> > +     * The low order 2 bits are the link pointer (Type II interrupts).
> > +     * Shift back to get a valid IRQ server.
> > +     */
> > +    server >>= 2;
> > +
> > +    switch (pq) {
> > +    case 0: /* 00 */
> > +        if (prio == 0xff) {
> > +            /* Masked, set Q */
> > +            phb3_msi_set_q(msi, srcno);
> > +        } else {
> > +            /* Enabled, set P and send */
> > +            phb3_msi_set_p(msi, srcno, gen);
> > +            icp_irq(ics, server, srcno + ics->offset, prio);
> > +        }
> > +        break;
> > +    case 2: /* 10 */
> > +        /* Already pending, set Q */
> > +        phb3_msi_set_q(msi, srcno);
> > +        break;
> > +    case 1: /* 01 */
> > +    case 3: /* 11 */
> > +    default:
> > +        /* Just drop stuff if Q already set */
> > +        break;
> > +    }
> > +}
> > +
> > +static void phb3_msi_set_irq(void *opaque, int srcno, int val)
> > +{
> > +    Phb3MsiState *msi = PHB3_MSI(opaque);
> > +
> > +    if (val) {
> > +        phb3_msi_try_send(msi, srcno, false);
> > +    }
> > +}
> 
> [ ... ]
>  
> > +static void phb3_msi_resend(ICSState *ics)
> > +{
> > +    Phb3MsiState *msi = PHB3_MSI(ics);
> > +    unsigned int i, j;
> > +
> > +    if (msi->rba_sum == 0) {
> > +        return;
> > +    }
> > +
> > +    for (i = 0; i < 32; i++) {
> > +        if ((msi->rba_sum & (1u << i)) == 0) {
> > +            continue;
> > +        }
> > +        msi->rba_sum &= ~(1u << i);
> > +        for (j = 0; j < 64; j++) {
> > +            if ((msi->rba[i] & (1ull << j)) == 0) {
> > +                continue;
> > +            }
> > +            msi->rba[i] &= ~(1u << j);
> > +            phb3_msi_try_send(msi, i * 64 + j, true);
> > +        }
> > +    }
> > +}
> 
>