qemu-kvm: require 4K aligned resource size for memory

qemu-kvm: require 4K aligned resource size for memory

[Michael S. Tsirkin]

KVM does not virtualize low address bits for memory accesses, so we must
require that PCI BAR size is a multiple of 4K for passthrough to work
(this also guarantees that address is 4K aligned).

Users of recent linux kernels can force resource size up to 4K
using:

	commit 32a9a682bef2f6fce7026bd94d1ce20028b0e52d
	Author: Yuji Shimada <shimada-yxb@necst.nec.co.jp>
	Date:   Mon Mar 16 17:13:39 2009 +0900
	PCI: allow assignment of memory resources with a specified alignment

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 237060f..c2ef31f 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -381,6 +381,14 @@ static int assigned_dev_register_regions(PCIRegion *io_regions,
             int t = cur_region->type & IORESOURCE_PREFETCH
                 ? PCI_ADDRESS_SPACE_MEM_PREFETCH
                 : PCI_ADDRESS_SPACE_MEM;
+            if (cur_region->size & 0xFFF) {
+                fprintf(stderr, "Unable to assign device: PCI region %d "
+                        "at address 0x%llx has size 0x%x, "
+                        " which is not a multiple of 4K\n",
+                        i, (unsigned long long)cur_region->base_addr,
+                        cur_region->size);
+                return -1;
+            }
 
             /* map physical memory */
             pci_dev->v_addrs[i].e_physbase = cur_region->base_addr;

Re: qemu-kvm: require 4K aligned resource size for memory

[Chris Wright]

* Michael S. Tsirkin (mst@redhat.com) wrote:
> KVM does not virtualize low address bits for memory accesses, so we must
> require that PCI BAR size is a multiple of 4K for passthrough to work
> (this also guarantees that address is 4K aligned).
> 
> Users of recent linux kernels can force resource size up to 4K
> using:
> 
> 	commit 32a9a682bef2f6fce7026bd94d1ce20028b0e52d
> 	Author: Yuji Shimada <shimada-yxb@necst.nec.co.jp>
> 	Date:   Mon Mar 16 17:13:39 2009 +0900
> 	PCI: allow assignment of memory resources with a specified alignment
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> ---
> 
> diff --git a/hw/device-assignment.c b/hw/device-assignment.c
> index 237060f..c2ef31f 100644
> --- a/hw/device-assignment.c
> +++ b/hw/device-assignment.c
> @@ -381,6 +381,14 @@ static int assigned_dev_register_regions(PCIRegion *io_regions,
>              int t = cur_region->type & IORESOURCE_PREFETCH
>                  ? PCI_ADDRESS_SPACE_MEM_PREFETCH
>                  : PCI_ADDRESS_SPACE_MEM;
> +            if (cur_region->size & 0xFFF) {
> +                fprintf(stderr, "Unable to assign device: PCI region %d "
> +                        "at address 0x%llx has size 0x%x, "
> +                        " which is not a multiple of 4K\n",
> +                        i, (unsigned long long)cur_region->base_addr,
> +                        cur_region->size);
> +                return -1;
> +            }

should render this useless now shouldn't it?

           /* add offset */
            pci_dev->v_addrs[i].u.r_virtbase +=
                (cur_region->base_addr & 0xFFF);

thanks,
-chris

Re: qemu-kvm: require 4K aligned resource size for memory

[Michael S. Tsirkin]

On Wed, Oct 21, 2009 at 11:42:47PM -0700, Chris Wright wrote:
> * Michael S. Tsirkin (mst@redhat.com) wrote:
> > KVM does not virtualize low address bits for memory accesses, so we must
> > require that PCI BAR size is a multiple of 4K for passthrough to work
> > (this also guarantees that address is 4K aligned).
> > 
> > Users of recent linux kernels can force resource size up to 4K
> > using:
> > 
> > 	commit 32a9a682bef2f6fce7026bd94d1ce20028b0e52d
> > 	Author: Yuji Shimada <shimada-yxb@necst.nec.co.jp>
> > 	Date:   Mon Mar 16 17:13:39 2009 +0900
> > 	PCI: allow assignment of memory resources with a specified alignment
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > 
> > ---
> > 
> > diff --git a/hw/device-assignment.c b/hw/device-assignment.c
> > index 237060f..c2ef31f 100644
> > --- a/hw/device-assignment.c
> > +++ b/hw/device-assignment.c
> > @@ -381,6 +381,14 @@ static int assigned_dev_register_regions(PCIRegion *io_regions,
> >              int t = cur_region->type & IORESOURCE_PREFETCH
> >                  ? PCI_ADDRESS_SPACE_MEM_PREFETCH
> >                  : PCI_ADDRESS_SPACE_MEM;
> > +            if (cur_region->size & 0xFFF) {
> > +                fprintf(stderr, "Unable to assign device: PCI region %d "
> > +                        "at address 0x%llx has size 0x%x, "
> > +                        " which is not a multiple of 4K\n",
> > +                        i, (unsigned long long)cur_region->base_addr,
> > +                        cur_region->size);
> > +                return -1;
> > +            }
> 
> should render this useless now shouldn't it?
> 
>            /* add offset */
>             pci_dev->v_addrs[i].u.r_virtbase +=
>                 (cur_region->base_addr & 0xFFF);

Yes, we could go over the code and remove all alignment.
But I'd rather not in case we decide on another approach
in the future. And for upstream, all this code will have to
be rewritten anyway.

> thanks,
> -chris

Re: qemu-kvm: require 4K aligned resource size for memory

[Marcelo Tosatti]

On Tue, Oct 20, 2009 at 07:15:09PM +0200, Michael S. Tsirkin wrote:
> KVM does not virtualize low address bits for memory accesses, so we must
> require that PCI BAR size is a multiple of 4K for passthrough to work
> (this also guarantees that address is 4K aligned).
> 
> Users of recent linux kernels can force resource size up to 4K
> using:
> 
> 	commit 32a9a682bef2f6fce7026bd94d1ce20028b0e52d
> 	Author: Yuji Shimada <shimada-yxb@necst.nec.co.jp>
> 	Date:   Mon Mar 16 17:13:39 2009 +0900
> 	PCI: allow assignment of memory resources with a specified alignment
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Applied, thanks.