Re: [Qemu-devel] [Qemu-ppc] [PATCH qemu v2] spapr_pci: Advertise BAR reallocation capability

[Greg Kurz]

On Wed, 17 Jul 2019 17:06:36 +1000
Alexey Kardashevskiy <address@hidden> wrote:

> The pseries guests do not normally allocate PCI resources and rely on
> the system firmware doing so. Furthermore at least at some point in
> the past the pseries guests won't even allowed to change BARs, probably
> it is still the case for phyp. So since the initial commit we have [1]
> which prevents resource reallocation.
> 
> This is not a problem until we want specific BAR alignments, for example,
> PAGE_SIZE==64k to make sure we can still map MMIO BARs directly. For
> the boot time devices we handle this in SLOF [2] but since QEMU's RTAS
> does not allocate BARs, the guest does this instead and does not align
> BARs even if Linux is given pci=resource_alignment=16@pci:0:0 as
> PCI_PROBE_ONLY makes Linux ignore alignment requests.
> 
> ARM folks added a dial to control PCI_PROBE_ONLY via the device tree [3].
> This makes use of the dial to advertise to the guest that we can handle
> BAR reassignments. This limits the change to the latest pseries machine
> to avoid old guests explosion.
> 
> We do not remove the flag from [1] as pseries guests are still supported
> under phyp so having that removed may cause problems.
> 
> [1] 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/platforms/pseries/setup.c?h=v5.1#n773
> [2] 
> https://git.qemu.org/?p=SLOF.git;a=blob;f=board-qemu/slof/pci-phb.fs;h=06729bcf77a0d4e900c527adcd9befe2a269f65d;hb=HEAD#l338
> [3] 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f81c11af
> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> ---
> Changes:
> v2:
> * limited the change by a machine version
> 
> ---
>  include/hw/ppc/spapr.h |  1 +
>  hw/ppc/spapr.c         | 11 +++++++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 60553d32c4fa..11c8185b94a1 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -120,6 +120,7 @@ struct SpaprMachineClass {
>      bool legacy_irq_allocation;
>      bool broken_host_serial_model; /* present real host info to the guest */
>      bool pre_4_1_migration; /* don't migrate hpt-max-page-size */
> +    bool linux_pci_probe;
>  
>      void (*phb_placement)(SpaprMachineState *spapr, uint32_t index,
>                            uint64_t *buid, hwaddr *pio, 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 8783b433960c..734d759d65b3 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1162,6 +1162,7 @@ static void 
> spapr_dt_ov5_platform_support(SpaprMachineState *spapr, void *fdt,
>  static void spapr_dt_chosen(SpaprMachineState *spapr, void *fdt)
>  {
>      MachineState *machine = MACHINE(spapr);
> +    SpaprMachineClass *smc = SPAPR_MACHINE_GET_CLASS(machine);
>      int chosen;
>      const char *boot_device = machine->boot_order;
>      char *stdout_path = spapr_vio_stdout_path(spapr->vio_bus);
> @@ -1219,6 +1220,11 @@ static void spapr_dt_chosen(SpaprMachineState *spapr, 
> void *fdt)
>          _FDT(fdt_setprop_string(fdt, chosen, "stdout-path", stdout_path));
>      }
>  
> +    /* We can deal with BAR reallocation just fine, advertise it to the 
> guest */
> +    if (smc->linux_pci_probe) {
> +        _FDT(fdt_setprop_cell(fdt, chosen, "linux,pci-probe-only", 0));
> +    }
> +
>      spapr_dt_ov5_platform_support(spapr, fdt, chosen);
>  
>      g_free(stdout_path);
> @@ -4432,6 +4438,9 @@ static const TypeInfo spapr_machine_info = {
>  static void spapr_machine_4_2_class_options(MachineClass *mc)
>  {
>      /* Defaults for the latest behaviour inherited from the base class */
> +    SpaprMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
> +
> +    smc->linux_pci_probe = true;

As written in the comment, defaults for the latest behavior belong to the
base class, ie. this should go to spapr_machine_class_init().

>  }
>  
>  DEFINE_SPAPR_MACHINE(4_2, "4.2", true);
> @@ -4441,12 +4450,14 @@ DEFINE_SPAPR_MACHINE(4_2, "4.2", true);
>   */
>  static void spapr_machine_4_1_class_options(MachineClass *mc)
>  {
> +    SpaprMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
>      static GlobalProperty compat[] = {
>          /* Only allow 4kiB and 64kiB IOMMU pagesizes */
>          { TYPE_SPAPR_PCI_HOST_BRIDGE, "pgsz", "0x11000" },
>      };
>  
>      spapr_machine_4_2_class_options(mc);
> +    smc->linux_pci_probe = false;
>      compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));
>  }
>