| Message ID | 20221031131934.425448-5-berrange@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | hw: make TCO watchdog actually work by default for Q35 | expand |
On Mon, Oct 31, 2022 at 01:19:34PM +0000, Daniel P. Berrangé wrote: > The TCO watchdog implementation default behaviour from POV of the > guest OS relies on the initial values for two I/O ports: > > * TCO1_CNT == 0x0 > > Since bit 11 (TCO Timer Halt) is clear, the watchdog state > is considered to be initially running > > * GCS == 0x20 > > Since bit 5 (No Reboot) is set, the watchdog will not trigger > when the timer expires > > This is a safe default, because the No Reboot bit will prevent the > watchdog from triggering if the guest OS is unaware of its existance, > or is slow in configuring it. When a Linux guest initializes the TCO > watchdog, it will attempt to clear the "No Reboot" flag, and read the > value back. If the clear was honoured, the driver will treat this as > an indicator that the watchdog is functional and create the geust Typo: "guest" > watchdog device. > > QEMU implements a second "no reboot" flag, however, via pin straps > which overrides the behaviour of the guest controlled "no reboot" > flag: > > commit 5add35bec1e249bb5345a47008c8f298d4760be4 > Author: Paulo Alcantara <pcacjr@gmail.com> > Date: Sun Jun 28 14:58:58 2015 -0300 > > ich9: implement strap SPKR pin logic > > This second 'noreboot' pin was defaulted to high, which also inhibits > triggering of the requested watchdog actions, unless QEMU is launched > with the magic flag "-global ICH9-LPC.noreboot=false". > > This is a bad default as we are exposing a watchdog to every guest OS > using the q35 machine type, but preventing it from actually doing what > it is designed to do. What is worse is that the guest OS and its apps > have no way to know that the watchdog is never going to fire, due to > this second 'noreboot' pin. > > If a guest OS had no watchdog device at all, then apps whose operation > and/or data integrity relies on a watchdog can refuse to launch, and > alert the administrator of the problematic deployment. With Q35 machines > unconditionally exposing a watchdog though, apps will think their > deployment is correct but in fact have no protection at all. > > This patch flips the default of the second 'no reboot' flag, so that > configured watchdog actions will be honoured out of the box for the > 7.2 Q35 machine type onwards, if the guest enables use of the watchdog. > > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> Add Fixes: or some other reference to the BZs? We have a few! https://bugzilla.redhat.com/show_bug.cgi?id=2136889 https://bugzilla.redhat.com/show_bug.cgi?id=2080207 https://bugzilla.redhat.com/show_bug.cgi?id=2137346 (libvirt) > hw/i386/pc.c | 4 +++- > hw/isa/lpc_ich9.c | 2 +- > tests/qtest/tco-test.c | 2 +- > 3 files changed, 5 insertions(+), 3 deletions(-) > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index 3e86083db3..e814f62fc6 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -108,7 +108,9 @@ > { "qemu64-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, },\ > { "athlon-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, }, > > -GlobalProperty pc_compat_7_1[] = {}; > +GlobalProperty pc_compat_7_1[] = { > + { "ICH9-LPC", "noreboot", "true" }, > +}; > const size_t pc_compat_7_1_len = G_N_ELEMENTS(pc_compat_7_1); > > GlobalProperty pc_compat_7_0[] = {}; > diff --git a/hw/isa/lpc_ich9.c b/hw/isa/lpc_ich9.c > index 66062a344c..f9ce2ee1dc 100644 > --- a/hw/isa/lpc_ich9.c > +++ b/hw/isa/lpc_ich9.c > @@ -789,7 +789,7 @@ static const VMStateDescription vmstate_ich9_lpc = { > }; > > static Property ich9_lpc_properties[] = { > - DEFINE_PROP_BOOL("noreboot", ICH9LPCState, pin_strap.spkr_hi, true), > + DEFINE_PROP_BOOL("noreboot", ICH9LPCState, pin_strap.spkr_hi, false), > DEFINE_PROP_BOOL("smm-compat", ICH9LPCState, pm.smm_compat, false), > DEFINE_PROP_BIT64("x-smi-broadcast", ICH9LPCState, smi_host_features, > ICH9_LPC_SMI_F_BROADCAST_BIT, true), > diff --git a/tests/qtest/tco-test.c b/tests/qtest/tco-test.c > index 254f735370..caabcac6e5 100644 > --- a/tests/qtest/tco-test.c > +++ b/tests/qtest/tco-test.c > @@ -60,7 +60,7 @@ static void test_init(TestData *d) > QTestState *qs; > > qs = qtest_initf("-machine q35 %s %s", > - d->noreboot ? "" : "-global ICH9-LPC.noreboot=false", > + d->noreboot ? "-global ICH9-LPC.noreboot=true" : "", > !d->args ? "" : d->args); > qtest_irq_intercept_in(qs, "ioapic"); Acked-by: Richard W.M. Jones <rjones@redhat.com> Rich.
diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 3e86083db3..e814f62fc6 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -108,7 +108,9 @@ { "qemu64-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, },\ { "athlon-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, }, -GlobalProperty pc_compat_7_1[] = {}; +GlobalProperty pc_compat_7_1[] = { + { "ICH9-LPC", "noreboot", "true" }, +}; const size_t pc_compat_7_1_len = G_N_ELEMENTS(pc_compat_7_1); GlobalProperty pc_compat_7_0[] = {}; diff --git a/hw/isa/lpc_ich9.c b/hw/isa/lpc_ich9.c index 66062a344c..f9ce2ee1dc 100644 --- a/hw/isa/lpc_ich9.c +++ b/hw/isa/lpc_ich9.c @@ -789,7 +789,7 @@ static const VMStateDescription vmstate_ich9_lpc = { }; static Property ich9_lpc_properties[] = { - DEFINE_PROP_BOOL("noreboot", ICH9LPCState, pin_strap.spkr_hi, true), + DEFINE_PROP_BOOL("noreboot", ICH9LPCState, pin_strap.spkr_hi, false), DEFINE_PROP_BOOL("smm-compat", ICH9LPCState, pm.smm_compat, false), DEFINE_PROP_BIT64("x-smi-broadcast", ICH9LPCState, smi_host_features, ICH9_LPC_SMI_F_BROADCAST_BIT, true), diff --git a/tests/qtest/tco-test.c b/tests/qtest/tco-test.c index 254f735370..caabcac6e5 100644 --- a/tests/qtest/tco-test.c +++ b/tests/qtest/tco-test.c @@ -60,7 +60,7 @@ static void test_init(TestData *d) QTestState *qs; qs = qtest_initf("-machine q35 %s %s", - d->noreboot ? "" : "-global ICH9-LPC.noreboot=false", + d->noreboot ? "-global ICH9-LPC.noreboot=true" : "", !d->args ? "" : d->args); qtest_irq_intercept_in(qs, "ioapic");
The TCO watchdog implementation default behaviour from POV of the guest OS relies on the initial values for two I/O ports: * TCO1_CNT == 0x0 Since bit 11 (TCO Timer Halt) is clear, the watchdog state is considered to be initially running * GCS == 0x20 Since bit 5 (No Reboot) is set, the watchdog will not trigger when the timer expires This is a safe default, because the No Reboot bit will prevent the watchdog from triggering if the guest OS is unaware of its existance, or is slow in configuring it. When a Linux guest initializes the TCO watchdog, it will attempt to clear the "No Reboot" flag, and read the value back. If the clear was honoured, the driver will treat this as an indicator that the watchdog is functional and create the geust watchdog device. QEMU implements a second "no reboot" flag, however, via pin straps which overrides the behaviour of the guest controlled "no reboot" flag: commit 5add35bec1e249bb5345a47008c8f298d4760be4 Author: Paulo Alcantara <pcacjr@gmail.com> Date: Sun Jun 28 14:58:58 2015 -0300 ich9: implement strap SPKR pin logic This second 'noreboot' pin was defaulted to high, which also inhibits triggering of the requested watchdog actions, unless QEMU is launched with the magic flag "-global ICH9-LPC.noreboot=false". This is a bad default as we are exposing a watchdog to every guest OS using the q35 machine type, but preventing it from actually doing what it is designed to do. What is worse is that the guest OS and its apps have no way to know that the watchdog is never going to fire, due to this second 'noreboot' pin. If a guest OS had no watchdog device at all, then apps whose operation and/or data integrity relies on a watchdog can refuse to launch, and alert the administrator of the problematic deployment. With Q35 machines unconditionally exposing a watchdog though, apps will think their deployment is correct but in fact have no protection at all. This patch flips the default of the second 'no reboot' flag, so that configured watchdog actions will be honoured out of the box for the 7.2 Q35 machine type onwards, if the guest enables use of the watchdog. Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- hw/i386/pc.c | 4 +++- hw/isa/lpc_ich9.c | 2 +- tests/qtest/tco-test.c | 2 +- 3 files changed, 5 insertions(+), 3 deletions(-)