Re: [PATCH for-5.1] xhci: fix valid.max_access_size to access address registers

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 7/21/20 10:33 AM, Laurent Vivier wrote:
> QEMU XHCI advertises AC64 (64-bit addressing) but doesn't allow
> 64-bit mode access in "runtime" and "operational" MemoryRegionOps.
> 
> Set the max_access_size based on sizeof(dma_addr_t) as AC64 is set.
> 
> XHCI specs:
> "If the xHC supports 64-bit addressing (AC64 = ‘1’), then software
> should write 64-bit registers using only Qword accesses.  If a
> system is incapable of issuing Qword accesses, then writes to the
> 64-bit address fields shall be performed using 2 Dword accesses;
> low Dword-first, high-Dword second.  If the xHC supports 32-bit
> addressing (AC64 = ‘0’), then the high Dword of registers containing
> 64-bit address fields are unused and software should write addresses
> using only Dword accesses"

You only describe the WRITE path. Is the READ path similar?

> 
> The problem has been detected with SLOF, as linux kernel always accesses
> registers using 32-bit access even if AC64 is set and revealed by
> 5d971f9e6725 ("memory: Revert "memory: accept mismatching sizes in memory_region_access_valid"")
> 
> Suggested-by: Alexey Kardashevskiy <aik@au1.ibm.com>
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  hw/usb/hcd-xhci.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
> index b330e36fe6cc..67a18fe2b64c 100644
> --- a/hw/usb/hcd-xhci.c
> +++ b/hw/usb/hcd-xhci.c
> @@ -3184,7 +3184,7 @@ static const MemoryRegionOps xhci_oper_ops = {
>      .read = xhci_oper_read,
>      .write = xhci_oper_write,
>      .valid.min_access_size = 4,
> -    .valid.max_access_size = 4,
> +    .valid.max_access_size = sizeof(dma_addr_t),
>      .endianness = DEVICE_LITTLE_ENDIAN,
>  };
>  
> @@ -3200,7 +3200,7 @@ static const MemoryRegionOps xhci_runtime_ops = {
>      .read = xhci_runtime_read,
>      .write = xhci_runtime_write,
>      .valid.min_access_size = 4,
> -    .valid.max_access_size = 4,
> +    .valid.max_access_size = sizeof(dma_addr_t),
>      .endianness = DEVICE_LITTLE_ENDIAN,
>  };

I wonder if we shouldn't check the access size now, something like:

bool xhci_check_access_size(void *opaque, hwaddr addr,
                            unsigned size, bool is_write,
                            MemTxAttrs attrs);
{
    XHCIState *xhci = opaque;

    /* FIXME only for is_write??? */
    return xhci->ac64 || size == 4;
}

And add to both MemoryRegionOps:

       .accepts = xhci_check_access_size,