Re: [PATCH 1/4] s390x/pci: use a reserved ID for the default PCI group

From: David Hildenbrand <david@redhat.com>
To: Matthew Rosato <mjrosato@linux.ibm.com>,
	thuth@redhat.com, qemu-s390x@nongnu.org, qemu-devel@nongnu.org
Cc: farman@linux.ibm.com, pmorel@linux.ibm.com, cohuck@redhat.com,
	richard.henderson@linaro.org, pasic@linux.ibm.com,
	borntraeger@linux.ibm.com
Subject: Re: [PATCH 1/4] s390x/pci: use a reserved ID for the default PCI group
Date: Thu, 2 Dec 2021 17:43:42 +0100	[thread overview]
Message-ID: <123ecaef-0f76-614c-2f6d-cdb824a84f56@redhat.com> (raw)
In-Reply-To: <20211202164110.326947-2-mjrosato@linux.ibm.com>

On 02.12.21 17:41, Matthew Rosato wrote:
> The current default PCI group being used can technically collide with a
> real group ID passed from a hostdev.  Let's instead use a group ID that comes
> from a special pool that is architected to be reserved for simulated devices.
> 
> Fixes: 28dc86a072 ("s390x/pci: use a PCI Group structure")
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
>  include/hw/s390x/s390-pci-bus.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/hw/s390x/s390-pci-bus.h b/include/hw/s390x/s390-pci-bus.h
> index aa891c178d..2727e7bdef 100644
> --- a/include/hw/s390x/s390-pci-bus.h
> +++ b/include/hw/s390x/s390-pci-bus.h
> @@ -313,7 +313,7 @@ typedef struct ZpciFmb {
>  } ZpciFmb;
>  QEMU_BUILD_BUG_MSG(offsetof(ZpciFmb, fmt0) != 48, "padding in ZpciFmb");
>  
> -#define ZPCI_DEFAULT_FN_GRP 0x20
> +#define ZPCI_DEFAULT_FN_GRP 0xFF
>  typedef struct S390PCIGroup {
>      ClpRspQueryPciGrp zpci_group;
>      int id;
> 

What happens if we migrate a VM from old to new QEMU? Won't the guest be
able to observe the change?

-- 
Thanks,

David / dhildenb