linux-kernel - Re: [PATCH 3/3] usb: xhci: Notify xen when DbC is unsafe to use

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Date:   Wed, 12 May 2021 08:59:59 -0600
From:   Connor Davis <connojdavis@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        xen-devel@...ts.xenproject.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] usb: xhci: Notify xen when DbC is unsafe to use

On May 12, 21, Greg Kroah-Hartman wrote:
> On Tue, May 11, 2021 at 06:18:21PM -0600, Connor Davis wrote:
> > When running as a dom0 guest on Xen, check if the USB3 debug
> > capability is enabled before xHCI reset, suspend, and resume. If it
> > is, call xen_dbgp_reset_prep() to notify Xen that it is unsafe to touch
> > MMIO registers until the next xen_dbgp_external_startup().
> >
> > This notification allows Xen to avoid undefined behavior resulting
> > from MMIO access when the host controller's CNR bit is set or when
> > the device transitions to D3hot.
> >
> > Signed-off-by: Connor Davis <connojdavis@...il.com>
> > ---
> >  drivers/usb/host/xhci-dbgcap.h |  6 ++++
> >  drivers/usb/host/xhci.c        | 57 ++++++++++++++++++++++++++++++++++
> >  drivers/usb/host/xhci.h        |  1 +
> >  3 files changed, 64 insertions(+)
> >
> > diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h
> > index c70b78d504eb..24784b82a840 100644
> > --- a/drivers/usb/host/xhci-dbgcap.h
> > +++ b/drivers/usb/host/xhci-dbgcap.h
> > @@ -227,4 +227,10 @@ static inline int xhci_dbc_resume(struct xhci_hcd *xhci)
> >  	return 0;
> >  }
> >  #endif /* CONFIG_USB_XHCI_DBGCAP */
> > +
> > +#ifdef CONFIG_XEN_DOM0
> > +int xen_dbgp_reset_prep(struct usb_hcd *hcd);
> > +int xen_dbgp_external_startup(struct usb_hcd *hcd);
> > +#endif /* CONFIG_XEN_DOM0 */
> > +
> >  #endif /* __LINUX_XHCI_DBGCAP_H */
> > diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> > index ca9385d22f68..afe44169183f 100644
> > --- a/drivers/usb/host/xhci.c
> > +++ b/drivers/usb/host/xhci.c
> > @@ -37,6 +37,57 @@ static unsigned long long quirks;
> >  module_param(quirks, ullong, S_IRUGO);
> >  MODULE_PARM_DESC(quirks, "Bit flags for quirks to be enabled as default");
> >
> > +#ifdef CONFIG_XEN_DOM0
> > +#include <xen/xen.h>
>
> <snip>
>
> Can't this #ifdef stuff go into a .h file?
>

Yep, will clean that up in v2.

> thanks,
>
> greg k-h

Thanks,
Connor