Re: [Qemu-devel] [PATCH] x86: ioapic: upgrade emulated IOAPIC to ver 0x20

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 25, 2016 at 07:36:24PM +0800, Peter Xu wrote:
> IOMMU IR and IOAPIC legacy devices (e.g., e1000) cannot work well
> together with some old Linux kernels (upstream before v4.0, or any
> released RHEL kernels). This patch fixes it.
> 
> The problem is that: some old linux kernels (with IR enabled) only
> support IOAPIC chips with version 0x20. New kernels after commit d32932d
> ("x86/irq: Convert IOAPIC to use hierarchical irqdomain interfaces")
> fixed this problem. To make sure we can work with even old kernels,
> let's upgrade our IOAPIC to version 0x20.
> 
> This patch is only useful when vIOMMU IR is enabled (which still do not
> support kernel IOAPIC). So here we are only upgrading QEMU IOAPIC chip
> to version 0x20. For kernel based IOAPIC, the version will still be
> 0x11.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

As a minimum, we need to make sure not to change this for
old machine types.

Given the timing, limiting this for when IR is enabled
would be a good idea I think.

> ---
>  hw/intc/ioapic.c                  | 6 ++++++
>  include/hw/i386/ioapic_internal.h | 3 ++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
> index 2d3282a..361c37c 100644
> --- a/hw/intc/ioapic.c
> +++ b/hw/intc/ioapic.c
> @@ -354,6 +354,12 @@ ioapic_mem_write(void *opaque, hwaddr addr, uint64_t val,
>              }
>          }
>          break;
> +    case IOAPIC_EOI:
> +        if (size != 4) {
> +            break;
> +        }
> +        ioapic_eoi_broadcast(val);
> +        break;
>      }
>  
>      ioapic_update_kvm_routes(s);


I'd add a code comment saying this is for 0x20 only.

> diff --git a/include/hw/i386/ioapic_internal.h b/include/hw/i386/ioapic_internal.h
> index d89ea1b..9654a93 100644
> --- a/include/hw/i386/ioapic_internal.h
> +++ b/include/hw/i386/ioapic_internal.h
> @@ -29,7 +29,7 @@
>  
>  #define MAX_IOAPICS                     1
>  
> -#define IOAPIC_VERSION                  0x11
> +#define IOAPIC_VERSION                  0x20
>  
>  #define IOAPIC_LVT_DEST_SHIFT           56
>  #define IOAPIC_LVT_DEST_IDX_SHIFT       48
> @@ -71,6 +71,7 @@
>  
>  #define IOAPIC_IOREGSEL                 0x00
>  #define IOAPIC_IOWIN                    0x10
> +#define IOAPIC_EOI                      0x40
>  
>  #define IOAPIC_REG_ID                   0x00
>  #define IOAPIC_REG_VER                  0x01
> -- 
> 2.4.11
>