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Message-ID: <20180515180104.646cba0c.cohuck@redhat.com>
Date: Tue, 15 May 2018 18:01:04 +0200
From: Cornelia Huck <cohuck@...hat.com>
To: Pierre Morel <pmorel@...ux.ibm.com>
Cc: Dong Jia Shi <bjsdjshi@...ux.ibm.com>,
Halil Pasic <pasic@...ux.ibm.com>, linux-s390@...r.kernel.org,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
qemu-s390x@...gnu.org, qemu-devel@...gnu.org
Subject: Re: [PATCH RFC 1/2] vfio-ccw: forward halt/clear to device if
supported
On Fri, 11 May 2018 11:53:52 +0200
Pierre Morel <pmorel@...ux.ibm.com> wrote:
> On 09/05/2018 17:49, Cornelia Huck wrote:
> > The initial version of vfio-ccw did not support forwarding of the
> > halt or clear functions to the device, and we had to emulate them
> > instead.
> >
> > For versions of the vfio-ccw kernel implementation that indeed do
> > support halt/clear (by indicating them in the fctl of the scsw in
> > the io_region), we can simply start making use of it. If the kernel
> > does not support handling halt/clear, fall back to emulation.
> >
> > Signed-off-by: Cornelia Huck <cohuck@...hat.com>
> > ---
> > hw/s390x/css.c | 32 ++++++++++++++++++++++++++++----
> > hw/vfio/ccw.c | 11 +++++++++--
> > include/hw/s390x/css.h | 10 +++++++---
> > 3 files changed, 44 insertions(+), 9 deletions(-)
> >
> > diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> > index 301bf1772f..b6727d0607 100644
> > --- a/hw/s390x/css.c
> > +++ b/hw/s390x/css.c
> > @@ -1180,6 +1180,16 @@ static void sch_handle_start_func_virtual(SubchDev *sch)
> >
> > }
> >
> > +static IOInstEnding sch_handle_clear_func_passthrough(SubchDev *sch)
> > +{
> > + return s390_ccw_cmd_request(sch);
> > +}
> > +
> > +static IOInstEnding sch_handle_halt_func_passthrough(SubchDev *sch)
> > +{
> > + return s390_ccw_cmd_request(sch);
> > +}
> > +
> > static IOInstEnding sch_handle_start_func_passthrough(SubchDev *sch)
> > {
> >
> > @@ -1233,13 +1243,27 @@ IOInstEnding do_subchannel_work_virtual(SubchDev *sch)
> > IOInstEnding do_subchannel_work_passthrough(SubchDev *sch)
> > {
> > SCSW *s = &sch->curr_status.scsw;
> > + static bool no_halt_clear;
> >
> > + /* if the kernel does not support halt/clear, fall back to emulation */
> > if (s->ctrl & SCSW_FCTL_CLEAR_FUNC) {
> > - /* TODO: Clear handling */
> > - sch_handle_clear_func(sch);
> > + if (no_halt_clear) {
> > + sch_handle_clear_func(sch);
> > + } else {
> > + if (sch_handle_clear_func_passthrough(sch) == IOINST_OPNOTSUPP) {
> > + no_halt_clear = true;
> > + sch_handle_halt_func(sch);
> > + }
> > + }
> > } else if (s->ctrl & SCSW_FCTL_HALT_FUNC) {
> > - /* TODO: Halt handling */
> > - sch_handle_halt_func(sch);
> > + if (no_halt_clear) {
> > + sch_handle_halt_func(sch);
> > + } else {
> > + if (sch_handle_halt_func_passthrough(sch) == IOINST_OPNOTSUPP) {
> > + no_halt_clear = true;
> > + sch_handle_halt_func(sch);
> > + }
> > + }
> > } else if (s->ctrl & SCSW_FCTL_START_FUNC) {
> > return sch_handle_start_func_passthrough(sch);
> > }
> > diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
> > index e67392c5f9..247901ae41 100644
> > --- a/hw/vfio/ccw.c
> > +++ b/hw/vfio/ccw.c
> > @@ -60,6 +60,7 @@ static IOInstEnding vfio_ccw_handle_request(SubchDev *sch)
> >
> > memset(region, 0, sizeof(*region));
> >
> > + /* orb is only valid for ssch, but does not hurt for other functions */
> > memcpy(region->orb_area, &sch->orb, sizeof(ORB));
> > memcpy(region->scsw_area, &sch->curr_status.scsw, sizeof(SCSW));
> >
> > @@ -70,8 +71,12 @@ again:
> > if (errno == EAGAIN) {
> > goto again;
> > }
> > - error_report("vfio-ccw: wirte I/O region failed with errno=%d", errno);
> > - ret = -errno;
> > + /* handle not supported operations like halt/clear on older kernels */
> > + if (ret != -EOPNOTSUPP) {
> > + error_report("vfio-ccw: write I/O region failed with errno=%d",
> > + errno);
> > + ret = -errno;
> > + }
> > } else {
> > ret = region->ret_code;
> > }
> > @@ -83,6 +88,8 @@ again:
> > case -ENODEV:
> > case -EACCES:
> > return IOINST_CC_NOT_OPERATIONAL;
> > + case -EOPNOTSUPP:
> > + return IOINST_OPNOTSUPP;
> > case -EFAULT:
> > default:
> > sch_gen_unit_exception(sch);
> > diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> > index 35facb47d2..e33f26882b 100644
> > --- a/include/hw/s390x/css.h
> > +++ b/include/hw/s390x/css.h
> > @@ -100,9 +100,11 @@ typedef struct CcwDataStream {
> > } CcwDataStream;
> >
> > /*
> > - * IO instructions conclude according to this. Currently we have only
> > - * cc codes. Valid values are 0, 1, 2, 3 and the generic semantic for
> > + * IO instructions conclude according to this. One class of values are
> > + * cc codes: Valid values are 0, 1, 2, 3 and the generic semantic for
> > * IO instructions is described briefly. For more details consult the PoP.
> > + * Additionally, other endings may occur due to internal processing errors
> > + * like lack of support for an operation.
> > */
> > typedef enum IOInstEnding {
> > /* produced expected result */
> > @@ -112,7 +114,9 @@ typedef enum IOInstEnding {
> > /* inst. ineffective because busy with previously initiated function */
> > IOINST_CC_BUSY = 2,
> > /* inst. ineffective because not operational */
> > - IOINST_CC_NOT_OPERATIONAL = 3
> > + IOINST_CC_NOT_OPERATIONAL = 3,
> > + /* internal: operation not supported */
> > + IOINST_OPNOTSUPP = 4
> > } IOInstEnding;
> >
> > typedef struct SubchDev SubchDev;
>
>
> Couldn't we introduce ABI versioning ?
Can you elaborate what you're referring to?
If you mean checking capabilities of the kernel or so: If we can avoid
that and just try (and stop if it does not work), I'd prefer that (no
dependencies).
The IOINST_OPNOTSUPP is a bit ugly, but I did not see a more elegant
way to pass 'not supported' up to the caller.
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