Re: [Qemu-devel] [PATCH repost] ahci: fix win7 hang on boot

[Paolo Bonzini <pbonzini@redhat.com>]

Il 28/10/2013 20:01, Michael S. Tsirkin ha scritto:
> From: Alexander Graf <agraf@suse.de>
> 
> When AHCI executes an asynchronous IDE command, it checked DRDY without
> checking either DRQ or BSY.  This sometimes caused interrupt to be sent
> before command is actually completed.
> 
> This resulted in a race condition: if guest then managed to access the
> device before command has completed, it would hang waiting for an
> interrupt.
> This was observed with windows 7 guests.
> 
> To fix, check for DRQ or BSY in additiona to DRDY, if set,
> the command is asynchronous so delay the interrupt until
> asynchronous done callback is invoked.
> 
> Reported-by: Michael S. Tsirkin <mst@redhat.com>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Tested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> ---
>  hw/ide/ahci.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> index a8be62c..fbea9e8 100644
> --- a/hw/ide/ahci.c
> +++ b/hw/ide/ahci.c
> @@ -961,7 +961,8 @@ static int handle_cmd(AHCIState *s, int port, int slot)
>          /* We're ready to process the command in FIS byte 2. */
>          ide_exec_cmd(&s->dev[port].port, cmd_fis[2]);
>  
> -        if (s->dev[port].port.ifs[0].status & READY_STAT) {
> +        if ((s->dev[port].port.ifs[0].status & (READY_STAT|DRQ_STAT|BUSY_STAT)) ==
> +            READY_STAT) {
>              ahci_write_fis_d2h(&s->dev[port], cmd_fis);
>          }
>      }
> 

While the patch fixes the symptom, I think it is only a bandaid.

There is no reason why the async_cmd_done should be restricted to
asynchronous commands.  If synchronous commands are made to go through
the async_cmd_done callback, you'll automatically get the D2H FIS
written for all commands.

It's good for 1.7, but let's revisit it for 1.8.

Paolo