|
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v4 11/11] drivers/char: allow driving the rest of XHCI by a domain while Xen uses DbC
On Wed, Aug 17, 2022 at 05:08:35PM +0200, Jan Beulich wrote:
> On 13.08.2022 03:39, Marek Marczykowski-Górecki wrote:
> > --- a/docs/misc/xen-command-line.pandoc
> > +++ b/docs/misc/xen-command-line.pandoc
> > @@ -724,7 +724,7 @@ Available alternatives, with their meaning, are:
> >
> > ### dbgp
> > > `= ehci[ <integer> | @pci<bus>:<slot>.<func> ]`
> > -> `= xhci[ <integer> | @pci<bus>:<slot>.<func> ]`
> > +> `= xhci[ <integer> | @pci<bus>:<slot>.<func> ][,share=<bool>|hwdom]`
> >
> > Specify the USB controller to use, either by instance number (when going
> > over the PCI busses sequentially) or by PCI device (must be on segment 0).
> > @@ -732,6 +732,19 @@ over the PCI busses sequentially) or by PCI device
> > (must be on segment 0).
> > Use `ehci` for EHCI debug port, use `xhci` for XHCI debug capability.
> > XHCI driver will wait indefinitely for the debug host to connect - make
> > sure the cable is connected.
> > +The `share` option for xhci controls who else can use the controller:
> > +* `no`: use the controller exclusively for console, even hardware domain
> > + (dom0) cannot use it
> > +* `hwdom`: hardware domain may use the controller too, ports not used for
> > debug
> > + console will be available for normal devices; this is the default
> > +* `yes`: the controller can be assigned to any domain; it is not safe to
> > assign
> > + the controller to untrusted domain
> > +
> > +Choosing `share=hwdom` (the default) or `share=no` allows a domain to
> > reset the
>
> DYM "... or `share=yes` ..." here?
Yes.
> > --- a/xen/drivers/char/xhci-dbc.c
> > +++ b/xen/drivers/char/xhci-dbc.c
> > @@ -23,6 +23,7 @@
> > #include <xen/iommu.h>
> > #include <xen/mm.h>
> > #include <xen/param.h>
> > +#include <xen/rangeset.h>
> > #include <xen/serial.h>
> > #include <xen/timer.h>
> > #include <xen/types.h>
> > @@ -232,6 +233,14 @@ struct dbc_work_ring {
> > uint64_t dma;
> > };
> >
> > +enum xhci_share {
> > + XHCI_SHARE_NONE = 0,
> > +#ifdef CONFIG_XHCI_SHARE
> > + XHCI_SHARE_HWDOM,
> > + XHCI_SHARE_ANY
> > +#endif
> > +};
>
> Hmm, this suggests that Dom0 cannot use the controller without the Kconfig
> enabled, which I hope is not the case.
It is the case, because you requested reset quirk to be behind
"experimental" tag in kconfig. This quirk is (currently) necessary even
if just dom0 uses the controller.
I'm happy to include the quirk by default, but I got impression you
wouldn't accept it. And I'd rather avoid marking the whole driver as
"experimental" (which hides it unless you select UNSUPPORTED) just
because of a small code necessary to share it with dom0.
> But I notice that patch 1, which
> was committed already, still uses pci_ro_device() rather than
> pci_hide_device() (like ehci-dbgp.c does).
>
> > @@ -1128,10 +1181,34 @@ static void __init cf_check
> > dbc_uart_init_postirq(struct serial_port *port)
> > init_timer(&uart->timer, dbc_uart_poll, port, 0);
> > set_timer(&uart->timer, NOW() + MILLISECS(1));
> >
> > - if ( pci_ro_device(0, uart->dbc.sbdf.bus, uart->dbc.sbdf.devfn) )
> > - printk(XENLOG_WARNING
> > - "Failed to mark read-only %pp used for XHCI console\n",
> > - &uart->dbc.sbdf);
> > + switch ( uart->dbc.share )
> > + {
> > + case XHCI_SHARE_NONE:
> > + if ( pci_ro_device(0, uart->dbc.sbdf.bus, uart->dbc.sbdf.devfn) )
> > + printk(XENLOG_WARNING
> > + "Failed to mark read-only %pp used for XHCI console\n",
> > + &uart->dbc.sbdf);
> > + break;
> > +#ifdef CONFIG_XHCI_SHARE
> > + case XHCI_SHARE_HWDOM:
> > + if ( pci_hide_device(0, uart->dbc.sbdf.bus, uart->dbc.sbdf.devfn) )
> > + printk(XENLOG_WARNING
> > + "Failed to hide %pp used for XHCI console\n",
> > + &uart->dbc.sbdf);
> > + break;
> > + case XHCI_SHARE_ANY:
> > + /* Do not hide. */
> > + break;
> > +#endif
> > + }
> > +#ifdef CONFIG_X86
> > + if ( rangeset_add_range(mmio_ro_ranges,
> > + PFN_DOWN(uart->dbc.xhc_mmio_phys +
> > uart->dbc.xhc_dbc_offset),
> > + PFN_UP(uart->dbc.xhc_mmio_phys + uart->dbc.xhc_dbc_offset +
> > + sizeof(*uart->dbc.dbc_reg)) - 1) )
> > + printk(XENLOG_INFO
> > + "Error while adding MMIO range of device to
> > mmio_ro_ranges\n");
> > +#endif
>
> I did comment on this last part before. There very minimum that I'd expect
> to appear here is a comment as to the issue with other elements living on
> the same page which a domain's driver may actually find a need to write to.
> As said before - as soon as such a report would surface, we'd likely need
> to add write emulation support for the leading/traling parts of the page(s)
> that Xen doesn't use itself.
I did included paragraph in the commit message:
| In any case, to avoid Linux messing with the DbC, mark this MMIO area as
| read-only. This might cause issues for Linux's driver (if it tries to
| write something on the same page - like anoter xcap), but makes Xen's
| use safe. In practice, as of Linux 5.18, it seems to work without
| issues.
Do you want this as a code comment too?
> > @@ -1202,13 +1279,18 @@ void __init xhci_dbc_uart_init(void)
> > {
> > struct dbc_uart *uart = &dbc_uart;
> > struct dbc *dbc = &uart->dbc;
> > - const char *e;
> > + const char *e, *opt;
> >
> > if ( strncmp(opt_dbgp, "xhci", 4) )
> > return;
> >
> > memset(dbc, 0, sizeof(*dbc));
> >
> > +#ifdef CONFIG_XHCI_SHARE
> > + dbc->share = XHCI_SHARE_HWDOM;
> > +#endif
>
> I think it would be best if the default value was "0"; I can see though
> that "NONE" being zero also makse sense, if the enum was to be used in
> boolean context (which afaics it currently isn't).
>
> > + e = &opt_dbgp[4];
> > if ( isdigit(opt_dbgp[4]) )
> > {
> > dbc->xhc_num = simple_strtoul(opt_dbgp + 4, &e, 10);
> > @@ -1218,7 +1300,7 @@ void __init xhci_dbc_uart_init(void)
> > unsigned int bus, slot, func;
> >
> > e = parse_pci(opt_dbgp + 8, NULL, &bus, &slot, &func);
> > - if ( !e || *e )
> > + if ( !e || (*e && *e != ',') )
> > {
> > printk(XENLOG_ERR
> > "Invalid dbgp= PCI device spec: '%s'\n",
> > @@ -1228,6 +1310,41 @@ void __init xhci_dbc_uart_init(void)
> >
> > dbc->sbdf = PCI_SBDF(0, bus, slot, func);
> > }
> > + opt = e;
> > +
> > +#ifdef CONFIG_XHCI_SHARE
> > + /* other options */
> > + while ( *opt == ',' )
> > + {
> > + opt++;
> > + e = strchr(opt, ',');
> > + if ( !e )
> > + e = strchr(opt, '\0');
> > +
> > + if ( !strncmp(opt, "share=", 6) )
> > + {
> > + int val = parse_bool(opt + 6, e);
> > + if ( val == -1 && !cmdline_strcmp(opt + 6, "hwdom") )
>
> Nit: Blank line please between declaration(s) and statement(s).
>
> Any reason you're using parse_bool() and not parse_boolean() here?
> That would save you the open-coded strncmp() afaict.
I can probably use parse_boolean() too, but then handling "hwdom"
variant would be a bit weird. I could skip 'share=hwdom' parsing at all,
since that's default if the kconfig option is enabled, but I'm not sure
if that's a good idea.
> Finally a remark seeing the opt_dbgp use here and the identically
> named option in ehci-dbgp.c, taken together with your multiple-
> serial-consoles patch: Since the two option consumers are now
> different, they can't sensibly coexist anymore. There were issues
> already before - it doesn't seem to be possible this way to run
> EHCI and XHCI based consoles in parallel. (An exceptional case
> would be if <integer> for both was intended to be same number.)
> IOW I think one of the options needs renaming; it was a mistake of
> mine to not have pointed this out before committing patch 1.
> Following the name of the source file as well as e.g. the title
> here - maybe "dbc="?
Yes, I can rename the option here. That requires also registering new
SERHND_* and inventing new value for console= parameter (implemented in
serial_parse_handle()). "dbc" there too?
--
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
Attachment:
signature.asc
|
 |
Lists.xenproject.org is hosted with RackSpace, monitoring our |