Re: [Qemu-devel] [RFC PATCH 07/10] spapr_pci: Allow PCI host bridge DMA window to be configured

[Alexey Kardashevskiy]

On 09/24/2015 04:59 PM, Laurent Vivier wrote:
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On 24/09/2015 01:54, David Gibson wrote:
On Wed, Sep 23, 2015 at 08:55:01PM +0200, Laurent Vivier wrote:


On 17/09/2015 15:09, David Gibson wrote:
At present the PCI host bridge (PHB) for the pseries machine
type has a fixed DMA window from 0..1GB (in PCI address space)
which is mapped to real memory via the PAPR paravirtualized
IOMMU.

For better support of VFIO devices, we're going to want to
allow for different configurations of the DMA window.

Eventually we'll want to allow the guest itself to reconfigure
the window via the PAPR dynamic DMA window interface, but as a
preliminary this patch allows the user to reconfigure the
window with new properties on the PHB device.

Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> ---
hw/ppc/spapr_pci.c          | 7 +++++--
include/hw/pci-host/spapr.h | 3 +-- 2 files changed, 6
insertions(+), 4 deletions(-)

diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c index
b088491..622c4ac 100644 --- a/hw/ppc/spapr_pci.c +++
b/hw/ppc/spapr_pci.c @@ -1394,7 +1394,7 @@ static void
spapr_phb_finish_realize(sPAPRPHBState *sphb, Error **errp)
sPAPRTCETable *tcet; uint32_t nb_table;

-    nb_table = SPAPR_PCI_DMA32_SIZE >> SPAPR_TCE_PAGE_SHIFT; +
nb_table = sphb->dma_win_size >> SPAPR_TCE_PAGE_SHIFT; tcet =
spapr_tce_new_table(DEVICE(sphb), sphb->dma_liobn, 0,
SPAPR_TCE_PAGE_SHIFT, nb_table, false); if (!tcet) { @@ -1404,7
+1404,7 @@ static void spapr_phb_finish_realize(sPAPRPHBState
*sphb, Error **errp) }

/* Register default 32bit DMA window */ -
memory_region_add_subregion(&sphb->iommu_root, 0, +
memory_region_add_subregion(&sphb->iommu_root,
sphb->dma_win_addr, spapr_tce_get_iommu(tcet)); }

@@ -1437,6 +1437,9 @@ static Property spapr_phb_properties[] =
{ SPAPR_PCI_IO_WIN_SIZE),
DEFINE_PROP_BOOL("dynamic-reconfiguration", sPAPRPHBState,
dr_enabled, true), +    /* Default DMA window is 0..1GB */ +
DEFINE_PROP_UINT64("dma_win_addr", sPAPRPHBState, dma_win_addr,
0), +    DEFINE_PROP_UINT64("dma_win_size", sPAPRPHBState,
dma_win_size, 0x40000000), DEFINE_PROP_END_OF_LIST(), };

Add them too to the vmstate_spapr_pci ?

No.  At least, not just now.

This is the sort of configuration information that typically isn't
migrated, instead requiring the far end to be set up matching.
Which

I think this is the aim of VMSTATE_UINT64_EQUAL() ?

We use it only for things which cannot be set via the command line and 
ideally there should be no VMSTATE_*_EQUAL. If something can be set via the 
command line, then the management software (read - libvirt) runs QEMU with 
explicit parameters to guarantee that these are equal. Checking it in 
VMSTATE is too late when migrating with full disk copy - it takes a lot of 
time before the destination QEMU discovers that it cannot actually run.



is a problem, but not one within the scope of this patch series.
In any case just transferring the values wouldn't be enough - we'd
need post_load handlers to actually rewire the TCE table
accordingly.

We will need to do this once we add dynamic DMA window support,
but again, not in scope just now.

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--
Alexey