Re: [Qemu-devel] [PATCH v2 2/2] spapr_pci: make index property mandatory

[David Gibson]

On Thu, Sep 14, 2017 at 04:14:44PM +0200, Greg Kurz wrote:
> Creating several PHBs without index property confuses the DRC code
> and causes issues:
> - only the first index-less PHB is functional, the other ones will
>   silently ignore hotplugging of PCI devices
> - QEMU will even terminate if these PHBs have cold-plugged devices

So, this is true, but it's kind of missing the point; we could fix
those things if we wanted.  The real point here is that the non-index
option is more trouble than it's worth: it's difficult to use, keeps
requiring (potentially incompatible) changes when some new parameter
needs adding, and is awkward to check for collisions.

> qemu-system-ppc64: -device virtio-net,bus=pci2.0: an attached device
>  is still awaiting release
> 
> This happens because DR connectors for child PCI devices are created
> with a DRC index that is derived from the PHB's index property. If the
> PHBs are created without index, then the same value of -1 is used to
> compute the DRC indexes for both PHBs, hence causing the collision.
> 
> Also, the index property is used to compute the placement of the PHB's
> memory regions. It is limited to 31 or 255, depending on the machine
> type version. This fits well with the requirements of DRC indexes, which
> need the PHB index to be a 16-bit value.
> 
> This patch hence makes the index property mandatory. As a consequence,
> the PHB's memory regions and BUID are now always configured according
> to the index, and it is no longer possible to set them from the command
> line. We have to introduce a PHB instance init function to initialize
> the 64-bit window address to -1 because pseries-2.7 and older machines
> don't set it.
> 
> This DOES BREAK backwards compat, but we don't think the non-index
> PHB feature was used in practice (at least libvirt doesn't) and the
> simplification is worth it.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> v1->v2: - error out if mem64_win_pciaddr is set but mem64_win_size
>           isn't
>         - set mem64_win_addr to -1 for old configuration with 32-bit
>           window below 2G in spapr_phb_realize()
>         - drop instance init function
> 
> RFC->v1: - as suggested dy David, updated the changelog to explicitely
>            mention that we intentionally break backwards compat.
> ---
>  hw/ppc/spapr_pci.c |   53 
> +++++++++++-----------------------------------------
>  1 file changed, 11 insertions(+), 42 deletions(-)
> 
> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> index cf54160526fa..024638e18b53 100644
> --- a/hw/ppc/spapr_pci.c
> +++ b/hw/ppc/spapr_pci.c
> @@ -1523,16 +1523,6 @@ static void spapr_phb_realize(DeviceState *dev, Error 
> **errp)
>          sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(spapr);
>          Error *local_err = NULL;
>  
> -        if ((sphb->buid != (uint64_t)-1) || (sphb->dma_liobn[0] != 
> (uint32_t)-1)
> -            || (sphb->dma_liobn[1] != (uint32_t)-1 && windows_supported == 2)
> -            || (sphb->mem_win_addr != (hwaddr)-1)
> -            || (sphb->mem64_win_addr != (hwaddr)-1)
> -            || (sphb->io_win_addr != (hwaddr)-1)) {
> -            error_setg(errp, "Either \"index\" or other parameters must"
> -                       " be specified for PAPR PHB, not both");
> -            return;
> -        }
> -
>          smc->phb_placement(spapr, sphb->index,
>                             &sphb->buid, &sphb->io_win_addr,
>                             &sphb->mem_win_addr, &sphb->mem64_win_addr,
> @@ -1541,36 +1531,12 @@ static void spapr_phb_realize(DeviceState *dev, Error 
> **errp)
>              error_propagate(errp, local_err);
>              return;
>          }
> -    }
> -
> -    if (sphb->buid == (uint64_t)-1) {
> -        error_setg(errp, "BUID not specified for PHB");
> -        return;
> -    }
> -
> -    if ((sphb->dma_liobn[0] == (uint32_t)-1) ||
> -        ((sphb->dma_liobn[1] == (uint32_t)-1) && (windows_supported > 1))) {
> -        error_setg(errp, "LIOBN(s) not specified for PHB");
> -        return;
> -    }
> -
> -    if (sphb->mem_win_addr == (hwaddr)-1) {
> -        error_setg(errp, "Memory window address not specified for PHB");
> -        return;
> -    }
> -
> -    if (sphb->io_win_addr == (hwaddr)-1) {
> -        error_setg(errp, "IO window address not specified for PHB");
> +    } else {
> +        error_setg(errp, "\"index\" for PAPR PHB is mandatory");
>          return;
>      }
>  
>      if (sphb->mem64_win_size != 0) {
> -        if (sphb->mem64_win_addr == (hwaddr)-1) {
> -            error_setg(errp,
> -                       "64-bit memory window address not specified for PHB");
> -            return;
> -        }
> -
>          if (sphb->mem_win_size > SPAPR_PCI_MEM32_WIN_SIZE) {
>              error_setg(errp, "32-bit memory window of size 0x%"HWADDR_PRIx
>                         " (max 2 GiB)", sphb->mem_win_size);

Some of these checks could probably just become assert()s now, where
they're things determined by the placement code and no longer have
parameters, a problem indicates a bug in the machine rather than a
user error.

> @@ -1581,6 +1547,9 @@ static void spapr_phb_realize(DeviceState *dev, Error 
> **errp)
>              /* 64-bit window defaults to identity mapping */
>              sphb->mem64_win_pciaddr = sphb->mem64_win_addr;
>          }
> +    } else if (sphb->mem64_win_pciaddr != (hwaddr) -1) {
> +        error_setg(errp, "64-bit memory window requires \"mem64_win_size\"");
> +        return;

Likewise this new one.

>      } else if (sphb->mem_win_size > SPAPR_PCI_MEM32_WIN_SIZE) {
>          /*
>           * For compatibility with old configuration, if no 64-bit MMIO
> @@ -1594,6 +1563,12 @@ static void spapr_phb_realize(DeviceState *dev, Error 
> **errp)
>          sphb->mem64_win_pciaddr =
>              SPAPR_PCI_MEM_WIN_BUS_OFFSET + SPAPR_PCI_MEM32_WIN_SIZE;
>          sphb->mem_win_size = SPAPR_PCI_MEM32_WIN_SIZE;
> +    } else {
> +        /* Old configuration with the 32-bit MMIO window <= 2GiB don't need a
> +         * 64-bit MMIO window.
> +         */

Wouldn't it be easier to just change the test below to check for size
!= 0 instead of checking for addr != -1 as it does now.

> +        sphb->mem64_win_addr = (hwaddr) -1;
> +        sphb->mem64_win_pciaddr = (hwaddr) -1;
>      }
>  
>      if (spapr_pci_find_phb(spapr, sphb->buid)) {
> @@ -1789,18 +1764,12 @@ static void spapr_phb_reset(DeviceState *qdev)
>  
>  static Property spapr_phb_properties[] = {
>      DEFINE_PROP_UINT32("index", sPAPRPHBState, index, -1),
> -    DEFINE_PROP_UINT64("buid", sPAPRPHBState, buid, -1),
> -    DEFINE_PROP_UINT32("liobn", sPAPRPHBState, dma_liobn[0], -1),
> -    DEFINE_PROP_UINT32("liobn64", sPAPRPHBState, dma_liobn[1], -1),
> -    DEFINE_PROP_UINT64("mem_win_addr", sPAPRPHBState, mem_win_addr, -1),
>      DEFINE_PROP_UINT64("mem_win_size", sPAPRPHBState, mem_win_size,
>                         SPAPR_PCI_MEM32_WIN_SIZE),
> -    DEFINE_PROP_UINT64("mem64_win_addr", sPAPRPHBState, mem64_win_addr, -1),
>      DEFINE_PROP_UINT64("mem64_win_size", sPAPRPHBState, mem64_win_size,
>                         SPAPR_PCI_MEM64_WIN_SIZE),
>      DEFINE_PROP_UINT64("mem64_win_pciaddr", sPAPRPHBState, mem64_win_pciaddr,
>                         -1),
> -    DEFINE_PROP_UINT64("io_win_addr", sPAPRPHBState, io_win_addr, -1),
>      DEFINE_PROP_UINT64("io_win_size", sPAPRPHBState, io_win_size,
>                         SPAPR_PCI_IO_WIN_SIZE),
>      DEFINE_PROP_BOOL("dynamic-reconfiguration", sPAPRPHBState, dr_enabled,
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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