* [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU]
@ 2021-10-08 20:38 Eric Farman
2021-10-08 20:38 ` [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter Eric Farman
` (2 more replies)
0 siblings, 3 replies; 11+ messages in thread
From: Eric Farman @ 2021-10-08 20:38 UTC (permalink / raw)
To: Halil Pasic, Cornelia Huck, Christian Borntraeger, Thomas Huth
Cc: Eric Farman, qemu-s390x, Richard Henderson, qemu-devel,
David Hildenbrand
I'm cleaning up some of the SIGP code in KVM and QEMU,
and would like to propose the following changes.
Patch 1 should be less concerning than its KVM counterpart,
since the CZAM bit in question is already present in QEMU.
Patch 2 provides some handshaking with KVM. Since QEMU
injects a Stop IRQ for a couple of the SIGP orders, we
can provide the flags associated with it, to provide some
direction for how KVM should process it.
While this has no dependency on the KVM code, the KVM series
that I'm working on in parallel is here:
https://lore.kernel.org/r/20211008203112.1979843-1-farman@linux.ibm.com/
Eric Farman (2):
s390x: sigp: Force Set Architecture to return Invalid Parameter
s390x/kvm: Pass SIGP Stop flags
target/s390x/kvm/kvm.c | 4 ++++
target/s390x/sigp.c | 18 +-----------------
2 files changed, 5 insertions(+), 17 deletions(-)
--
2.25.1
^ permalink raw reply [flat|nested] 11+ messages in thread* [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter 2021-10-08 20:38 [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Eric Farman @ 2021-10-08 20:38 ` Eric Farman 2021-10-09 5:40 ` Thomas Huth 2021-10-11 7:04 ` David Hildenbrand 2021-10-08 20:38 ` [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags Eric Farman 2021-10-12 6:58 ` [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Thomas Huth 2 siblings, 2 replies; 11+ messages in thread From: Eric Farman @ 2021-10-08 20:38 UTC (permalink / raw) To: Halil Pasic, Cornelia Huck, Christian Borntraeger, Thomas Huth Cc: Eric Farman, Janosch Frank, David Hildenbrand, Richard Henderson, qemu-devel, qemu-s390x According to the Principles of Operation, the SIGP Set Architecture order will return Incorrect State if some CPUs are not stopped, but only if the CZAM facility is not present. If it is, the order will return Invalid Parameter because the architecture mode cannot be changed. Since CZAM always exists when S390_FEAT_ZARCH exists, which in turn exists for every defined CPU model, we can simplify this code. Fixes: 075e52b81664 ("s390x/cpumodel: we are always in zarchitecture mode") Signed-off-by: Eric Farman <farman@linux.ibm.com> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Janosch Frank <frankja@linux.ibm.com> --- target/s390x/sigp.c | 18 +----------------- 1 file changed, 1 insertion(+), 17 deletions(-) diff --git a/target/s390x/sigp.c b/target/s390x/sigp.c index d57427ced8..51c727834c 100644 --- a/target/s390x/sigp.c +++ b/target/s390x/sigp.c @@ -428,26 +428,10 @@ static int handle_sigp_single_dst(S390CPU *cpu, S390CPU *dst_cpu, uint8_t order, static int sigp_set_architecture(S390CPU *cpu, uint32_t param, uint64_t *status_reg) { - CPUState *cur_cs; - S390CPU *cur_cpu; - bool all_stopped = true; - - CPU_FOREACH(cur_cs) { - cur_cpu = S390_CPU(cur_cs); - - if (cur_cpu == cpu) { - continue; - } - if (s390_cpu_get_state(cur_cpu) != S390_CPU_STATE_STOPPED) { - all_stopped = false; - } - } - *status_reg &= 0xffffffff00000000ULL; /* Reject set arch order, with czam we're always in z/Arch mode. */ - *status_reg |= (all_stopped ? SIGP_STAT_INVALID_PARAMETER : - SIGP_STAT_INCORRECT_STATE); + *status_reg |= SIGP_STAT_INVALID_PARAMETER; return SIGP_CC_STATUS_STORED; } -- 2.25.1 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter 2021-10-08 20:38 ` [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter Eric Farman @ 2021-10-09 5:40 ` Thomas Huth 2021-10-11 7:04 ` David Hildenbrand 1 sibling, 0 replies; 11+ messages in thread From: Thomas Huth @ 2021-10-09 5:40 UTC (permalink / raw) To: Eric Farman, Halil Pasic, Cornelia Huck, Christian Borntraeger Cc: qemu-devel, qemu-s390x, Richard Henderson, Janosch Frank, David Hildenbrand On 08/10/2021 22.38, Eric Farman wrote: > According to the Principles of Operation, the SIGP Set Architecture > order will return Incorrect State if some CPUs are not stopped, but > only if the CZAM facility is not present. If it is, the order will > return Invalid Parameter because the architecture mode cannot be > changed. > > Since CZAM always exists when S390_FEAT_ZARCH exists, which in turn > exists for every defined CPU model, we can simplify this code. > > Fixes: 075e52b81664 ("s390x/cpumodel: we are always in zarchitecture mode") > Signed-off-by: Eric Farman <farman@linux.ibm.com> > Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> > Reviewed-by: Janosch Frank <frankja@linux.ibm.com> > --- > target/s390x/sigp.c | 18 +----------------- > 1 file changed, 1 insertion(+), 17 deletions(-) > > diff --git a/target/s390x/sigp.c b/target/s390x/sigp.c > index d57427ced8..51c727834c 100644 > --- a/target/s390x/sigp.c > +++ b/target/s390x/sigp.c > @@ -428,26 +428,10 @@ static int handle_sigp_single_dst(S390CPU *cpu, S390CPU *dst_cpu, uint8_t order, > static int sigp_set_architecture(S390CPU *cpu, uint32_t param, > uint64_t *status_reg) > { > - CPUState *cur_cs; > - S390CPU *cur_cpu; > - bool all_stopped = true; > - > - CPU_FOREACH(cur_cs) { > - cur_cpu = S390_CPU(cur_cs); > - > - if (cur_cpu == cpu) { > - continue; > - } > - if (s390_cpu_get_state(cur_cpu) != S390_CPU_STATE_STOPPED) { > - all_stopped = false; > - } > - } > - > *status_reg &= 0xffffffff00000000ULL; > > /* Reject set arch order, with czam we're always in z/Arch mode. */ > - *status_reg |= (all_stopped ? SIGP_STAT_INVALID_PARAMETER : > - SIGP_STAT_INCORRECT_STATE); > + *status_reg |= SIGP_STAT_INVALID_PARAMETER; > return SIGP_CC_STATUS_STORED; > } Reviewed-by: Thomas Huth <thuth@redhat.com> By the way, I think we could now also get rid of SIGP_MODE_ESA_S390, SIGP_MODE_Z_ARCH_TRANS_ALL_PSW and SIGP_MODE_Z_ARCH_TRANS_CUR_PSW now (in a separate patch)... ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter 2021-10-08 20:38 ` [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter Eric Farman 2021-10-09 5:40 ` Thomas Huth @ 2021-10-11 7:04 ` David Hildenbrand 1 sibling, 0 replies; 11+ messages in thread From: David Hildenbrand @ 2021-10-11 7:04 UTC (permalink / raw) To: Eric Farman, Halil Pasic, Cornelia Huck, Christian Borntraeger, Thomas Huth Cc: qemu-s390x, Richard Henderson, qemu-devel, Janosch Frank On 08.10.21 22:38, Eric Farman wrote: > According to the Principles of Operation, the SIGP Set Architecture > order will return Incorrect State if some CPUs are not stopped, but > only if the CZAM facility is not present. If it is, the order will > return Invalid Parameter because the architecture mode cannot be > changed. > > Since CZAM always exists when S390_FEAT_ZARCH exists, which in turn > exists for every defined CPU model, we can simplify this code. > > Fixes: 075e52b81664 ("s390x/cpumodel: we are always in zarchitecture mode") > Signed-off-by: Eric Farman <farman@linux.ibm.com> > Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> > Reviewed-by: Janosch Frank <frankja@linux.ibm.com> Reviewed-by: David Hildenbrand <david@redhat.com> -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 11+ messages in thread
* [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags 2021-10-08 20:38 [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Eric Farman 2021-10-08 20:38 ` [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter Eric Farman @ 2021-10-08 20:38 ` Eric Farman 2021-10-11 7:09 ` David Hildenbrand 2021-10-12 6:58 ` [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Thomas Huth 2 siblings, 1 reply; 11+ messages in thread From: Eric Farman @ 2021-10-08 20:38 UTC (permalink / raw) To: Halil Pasic, Cornelia Huck, Christian Borntraeger, Thomas Huth Cc: Eric Farman, Janosch Frank, David Hildenbrand, Richard Henderson, qemu-devel, qemu-s390x When building a Stop IRQ to pass to KVM, we should incorporate the flags if handling the SIGP Stop and Store Status order. With that, KVM can reject other orders that are submitted for the same CPU while the operation is fully processed. Signed-off-by: Eric Farman <farman@linux.ibm.com> Acked-by: Janosch Frank <frankja@linux.ibm.com> --- target/s390x/kvm/kvm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c index 5b1fdb55c4..701b9ddc88 100644 --- a/target/s390x/kvm/kvm.c +++ b/target/s390x/kvm/kvm.c @@ -2555,6 +2555,10 @@ void kvm_s390_stop_interrupt(S390CPU *cpu) .type = KVM_S390_SIGP_STOP, }; + if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) { + irq.u.stop.flags = KVM_S390_STOP_FLAG_STORE_STATUS; + } + kvm_s390_vcpu_interrupt(cpu, &irq); } -- 2.25.1 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags 2021-10-08 20:38 ` [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags Eric Farman @ 2021-10-11 7:09 ` David Hildenbrand 2021-10-11 8:40 ` Christian Borntraeger 0 siblings, 1 reply; 11+ messages in thread From: David Hildenbrand @ 2021-10-11 7:09 UTC (permalink / raw) To: Eric Farman, Halil Pasic, Cornelia Huck, Christian Borntraeger, Thomas Huth Cc: qemu-s390x, Richard Henderson, qemu-devel, Janosch Frank On 08.10.21 22:38, Eric Farman wrote: > When building a Stop IRQ to pass to KVM, we should incorporate > the flags if handling the SIGP Stop and Store Status order. > With that, KVM can reject other orders that are submitted for > the same CPU while the operation is fully processed. > > Signed-off-by: Eric Farman <farman@linux.ibm.com> > Acked-by: Janosch Frank <frankja@linux.ibm.com> > --- > target/s390x/kvm/kvm.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c > index 5b1fdb55c4..701b9ddc88 100644 > --- a/target/s390x/kvm/kvm.c > +++ b/target/s390x/kvm/kvm.c > @@ -2555,6 +2555,10 @@ void kvm_s390_stop_interrupt(S390CPU *cpu) > .type = KVM_S390_SIGP_STOP, > }; > > + if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) { > + irq.u.stop.flags = KVM_S390_STOP_FLAG_STORE_STATUS; > + } > + KVM_S390_STOP_FLAG_STORE_STATUS tells KVM to perform the store status as well ... is that really what we want? Maybe we want a different (more generic) way to tell KVM that a CPU is temporarily busy for SIGP orders? -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags 2021-10-11 7:09 ` David Hildenbrand @ 2021-10-11 8:40 ` Christian Borntraeger 2021-10-11 9:21 ` David Hildenbrand 0 siblings, 1 reply; 11+ messages in thread From: Christian Borntraeger @ 2021-10-11 8:40 UTC (permalink / raw) To: David Hildenbrand, Eric Farman, Halil Pasic, Cornelia Huck, Thomas Huth Cc: qemu-s390x, Richard Henderson, qemu-devel, Janosch Frank Am 11.10.21 um 09:09 schrieb David Hildenbrand: > On 08.10.21 22:38, Eric Farman wrote: >> When building a Stop IRQ to pass to KVM, we should incorporate >> the flags if handling the SIGP Stop and Store Status order. >> With that, KVM can reject other orders that are submitted for >> the same CPU while the operation is fully processed. >> >> Signed-off-by: Eric Farman <farman@linux.ibm.com> >> Acked-by: Janosch Frank <frankja@linux.ibm.com> >> --- >> target/s390x/kvm/kvm.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c >> index 5b1fdb55c4..701b9ddc88 100644 >> --- a/target/s390x/kvm/kvm.c >> +++ b/target/s390x/kvm/kvm.c >> @@ -2555,6 +2555,10 @@ void kvm_s390_stop_interrupt(S390CPU *cpu) >> .type = KVM_S390_SIGP_STOP, >> }; >> + if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) { >> + irq.u.stop.flags = KVM_S390_STOP_FLAG_STORE_STATUS; >> + } >> + > > KVM_S390_STOP_FLAG_STORE_STATUS tells KVM to perform the store status as well ... is that really what we want? At least it should not hurt I guess. QEMU then does it again? > > Maybe we want a different (more generic) way to tell KVM that a CPU is temporarily busy for SIGP orders? > ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags 2021-10-11 8:40 ` Christian Borntraeger @ 2021-10-11 9:21 ` David Hildenbrand 2021-10-11 17:58 ` Eric Farman 0 siblings, 1 reply; 11+ messages in thread From: David Hildenbrand @ 2021-10-11 9:21 UTC (permalink / raw) To: Christian Borntraeger, Eric Farman, Halil Pasic, Cornelia Huck, Thomas Huth Cc: qemu-s390x, Richard Henderson, qemu-devel, Janosch Frank On 11.10.21 10:40, Christian Borntraeger wrote: > > > Am 11.10.21 um 09:09 schrieb David Hildenbrand: >> On 08.10.21 22:38, Eric Farman wrote: >>> When building a Stop IRQ to pass to KVM, we should incorporate >>> the flags if handling the SIGP Stop and Store Status order. >>> With that, KVM can reject other orders that are submitted for >>> the same CPU while the operation is fully processed. >>> >>> Signed-off-by: Eric Farman <farman@linux.ibm.com> >>> Acked-by: Janosch Frank <frankja@linux.ibm.com> >>> --- >>> target/s390x/kvm/kvm.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c >>> index 5b1fdb55c4..701b9ddc88 100644 >>> --- a/target/s390x/kvm/kvm.c >>> +++ b/target/s390x/kvm/kvm.c >>> @@ -2555,6 +2555,10 @@ void kvm_s390_stop_interrupt(S390CPU *cpu) >>> .type = KVM_S390_SIGP_STOP, >>> }; >>> + if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) { >>> + irq.u.stop.flags = KVM_S390_STOP_FLAG_STORE_STATUS; >>> + } >>> + >> >> KVM_S390_STOP_FLAG_STORE_STATUS tells KVM to perform the store status as well ... is that really what we want? > At least it should not hurt I guess. QEMU then does it again? The thing is, that before we officially completed the action in user space (and let other SIGP actions actually succeed in user space on the CPU), the target CPU will be reported as !busy in the kernel already. And before we even inject the stop interrupt, the CPU will be detected as !busy in the kernel. I guess it will fix some cases where we poll via SENSE if the stop and store happened, because the store *did* happen in the kernel and we'll simply store again in user space. However, I wonder if we want to handle it more generically: Properly flag a CPU as busy for SIGP when we start processing the order until we completed processing the order. That would allow to handle other SIGP operations in user space cleanly, without any chance for races with SENSE code running in the kernel. -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags 2021-10-11 9:21 ` David Hildenbrand @ 2021-10-11 17:58 ` Eric Farman 2021-10-11 18:07 ` David Hildenbrand 0 siblings, 1 reply; 11+ messages in thread From: Eric Farman @ 2021-10-11 17:58 UTC (permalink / raw) To: David Hildenbrand, Christian Borntraeger, Halil Pasic, Cornelia Huck, Thomas Huth Cc: qemu-s390x, Richard Henderson, qemu-devel, Janosch Frank On Mon, 2021-10-11 at 11:21 +0200, David Hildenbrand wrote: > On 11.10.21 10:40, Christian Borntraeger wrote: > > > > Am 11.10.21 um 09:09 schrieb David Hildenbrand: > > > On 08.10.21 22:38, Eric Farman wrote: > > > > When building a Stop IRQ to pass to KVM, we should incorporate > > > > the flags if handling the SIGP Stop and Store Status order. > > > > With that, KVM can reject other orders that are submitted for > > > > the same CPU while the operation is fully processed. > > > > > > > > Signed-off-by: Eric Farman <farman@linux.ibm.com> > > > > Acked-by: Janosch Frank <frankja@linux.ibm.com> > > > > --- > > > > target/s390x/kvm/kvm.c | 4 ++++ > > > > 1 file changed, 4 insertions(+) > > > > > > > > diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c > > > > index 5b1fdb55c4..701b9ddc88 100644 > > > > --- a/target/s390x/kvm/kvm.c > > > > +++ b/target/s390x/kvm/kvm.c > > > > @@ -2555,6 +2555,10 @@ void kvm_s390_stop_interrupt(S390CPU > > > > *cpu) > > > > .type = KVM_S390_SIGP_STOP, > > > > }; > > > > + if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) { > > > > + irq.u.stop.flags = KVM_S390_STOP_FLAG_STORE_STATUS; > > > > + } > > > > + > > > > > > KVM_S390_STOP_FLAG_STORE_STATUS tells KVM to perform the store > > > status as well ... is that really what we want? > > At least it should not hurt I guess. QEMU then does it again? > > The thing is, that before we officially completed the action in user > space (and let other SIGP actions actually succeed in user space on > the > CPU), the target CPU will be reported as !busy in the kernel > already. > And before we even inject the stop interrupt, the CPU will be > detected > as !busy in the kernel. I guess it will fix some cases where we poll > via > SENSE if the stop and store happened, because the store *did* happen > in > the kernel and we'll simply store again in user space. > > However, I wonder if we want to handle it more generically: Properly > flag a CPU as busy for SIGP when we start processing the order until > we > completed processing the order. That would allow to handle other > SIGP > operations in user space cleanly, without any chance for races with > SENSE code running in the kernel. > I think a generic solution would be ideal, but I'm wrestling with the race with the kernel's SENSE code. Today, handle_sigp_single_dst already checks to see if a CPU is currently processing an order and returns a CC2 when it does, but of course the kernel's SENSE code doesn't know that. We could flag the CPU as busy in the kernel when sending a SIGP to userspace, so that the SENSE code indicates BUSY, but then how do we know when userspace is finished and the CPU is no longer BUSY? Eric ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags 2021-10-11 17:58 ` Eric Farman @ 2021-10-11 18:07 ` David Hildenbrand 0 siblings, 0 replies; 11+ messages in thread From: David Hildenbrand @ 2021-10-11 18:07 UTC (permalink / raw) To: Eric Farman, Christian Borntraeger, Halil Pasic, Cornelia Huck, Thomas Huth Cc: qemu-s390x, Richard Henderson, qemu-devel, Janosch Frank On 11.10.21 19:58, Eric Farman wrote: > On Mon, 2021-10-11 at 11:21 +0200, David Hildenbrand wrote: >> On 11.10.21 10:40, Christian Borntraeger wrote: >>> >>> Am 11.10.21 um 09:09 schrieb David Hildenbrand: >>>> On 08.10.21 22:38, Eric Farman wrote: >>>>> When building a Stop IRQ to pass to KVM, we should incorporate >>>>> the flags if handling the SIGP Stop and Store Status order. >>>>> With that, KVM can reject other orders that are submitted for >>>>> the same CPU while the operation is fully processed. >>>>> >>>>> Signed-off-by: Eric Farman <farman@linux.ibm.com> >>>>> Acked-by: Janosch Frank <frankja@linux.ibm.com> >>>>> --- >>>>> target/s390x/kvm/kvm.c | 4 ++++ >>>>> 1 file changed, 4 insertions(+) >>>>> >>>>> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c >>>>> index 5b1fdb55c4..701b9ddc88 100644 >>>>> --- a/target/s390x/kvm/kvm.c >>>>> +++ b/target/s390x/kvm/kvm.c >>>>> @@ -2555,6 +2555,10 @@ void kvm_s390_stop_interrupt(S390CPU >>>>> *cpu) >>>>> .type = KVM_S390_SIGP_STOP, >>>>> }; >>>>> + if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) { >>>>> + irq.u.stop.flags = KVM_S390_STOP_FLAG_STORE_STATUS; >>>>> + } >>>>> + >>>> >>>> KVM_S390_STOP_FLAG_STORE_STATUS tells KVM to perform the store >>>> status as well ... is that really what we want? >>> At least it should not hurt I guess. QEMU then does it again? >> >> The thing is, that before we officially completed the action in user >> space (and let other SIGP actions actually succeed in user space on >> the >> CPU), the target CPU will be reported as !busy in the kernel >> already. >> And before we even inject the stop interrupt, the CPU will be >> detected >> as !busy in the kernel. I guess it will fix some cases where we poll >> via >> SENSE if the stop and store happened, because the store *did* happen >> in >> the kernel and we'll simply store again in user space. >> >> However, I wonder if we want to handle it more generically: Properly >> flag a CPU as busy for SIGP when we start processing the order until >> we >> completed processing the order. That would allow to handle other >> SIGP >> operations in user space cleanly, without any chance for races with >> SENSE code running in the kernel. >> > > I think a generic solution would be ideal, but I'm wrestling with the > race with the kernel's SENSE code. Today, handle_sigp_single_dst > already checks to see if a CPU is currently processing an order and > returns a CC2 when it does, but of course the kernel's SENSE code > doesn't know that. We could flag the CPU as busy in the kernel when > sending a SIGP to userspace, so that the SENSE code indicates BUSY, but > then how do we know when userspace is finished and the CPU is no longer > BUSY? I'd just add a new IOCTL for marking a CPU busy/!busy for SIGP from user space. You can then either let user space perform both actions (set+unset), or let the kernel automatically set "busy" and user space only clear "busy". You can define a new capability to enable the "automatically set busy when going to user space on sigp" -- might require some thoughts on some corner cases. Maybe there might be other scenarios in the future where we might want to set a CPU busy for sigp without that CPU triggering a sigp action itself (e.g., externally triggered reset of a CPU? Simulation of check-stop? store status?), so at least having a way to set/reset a CPU busy for SIGP might be valuable. Once we go to user space to process a SIGP, we usually don't care too much about some additional overhead due to 1 or 2 ioctls IMHO. -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] 2021-10-08 20:38 [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Eric Farman 2021-10-08 20:38 ` [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter Eric Farman 2021-10-08 20:38 ` [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags Eric Farman @ 2021-10-12 6:58 ` Thomas Huth 2 siblings, 0 replies; 11+ messages in thread From: Thomas Huth @ 2021-10-12 6:58 UTC (permalink / raw) To: Eric Farman; +Cc: QEMU Developers On 08/10/2021 22.38, Eric Farman wrote: > I'm cleaning up some of the SIGP code in KVM and QEMU, > and would like to propose the following changes. > > Patch 1 should be less concerning than its KVM counterpart, > since the CZAM bit in question is already present in QEMU. > > Patch 2 provides some handshaking with KVM. Since QEMU > injects a Stop IRQ for a couple of the SIGP orders, we > can provide the flags associated with it, to provide some > direction for how KVM should process it. > > While this has no dependency on the KVM code, the KVM series > that I'm working on in parallel is here: > > https://lore.kernel.org/r/20211008203112.1979843-1-farman@linux.ibm.com/ > > Eric Farman (2): > s390x: sigp: Force Set Architecture to return Invalid Parameter > s390x/kvm: Pass SIGP Stop flags > > target/s390x/kvm/kvm.c | 4 ++++ > target/s390x/sigp.c | 18 +----------------- > 2 files changed, 5 insertions(+), 17 deletions(-) > FYI, I've queued the first patch to my s390x-next branch: https://gitlab.com/thuth/qemu/-/commits/s390x-next ... for the second patch, I'll wait for the discussion to settle. Thomas ^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2021-10-12 6:59 UTC | newest] Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-10-08 20:38 [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Eric Farman 2021-10-08 20:38 ` [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter Eric Farman 2021-10-09 5:40 ` Thomas Huth 2021-10-11 7:04 ` David Hildenbrand 2021-10-08 20:38 ` [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags Eric Farman 2021-10-11 7:09 ` David Hildenbrand 2021-10-11 8:40 ` Christian Borntraeger 2021-10-11 9:21 ` David Hildenbrand 2021-10-11 17:58 ` Eric Farman 2021-10-11 18:07 ` David Hildenbrand 2021-10-12 6:58 ` [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Thomas Huth
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