Re: [PATCH] KVM: PPC: Book3S: Add support for H_IPOLL and H_XIRR_X in XICS emulation
On 05/29/2013 06:57:32 PM, Benjamin Herrenschmidt wrote: On Wed, 2013-05-29 at 18:38 -0500, Scott Wood wrote: > > Yes. I'd like to have them in. Their implementation is actually fairly > > trivial and they cannot be emulated by qemu if the rest of the XICS is > > in the kernel, so it's a problem. > > OK. Does it make more sense for you to take it as Paul suggested, or > for Gleb or Marcelo to pick it up directly? I'll take it. Acked-by: Scott Wood > Then rm_action should always be 0 for these hcalls, right? So there's > no correctness reason to keep the hcalls in separate switch > statements. You shave off a few cycles checking rm_action, at the cost > of needing to change kvmppc_xics_hcall() if a real-mode version of > these hcalls is ever done. No, because rm_action will also be 0 if the hcall was fully done in real mode (which can happen, that's our fast path), in which case we do *NOT* want to to be re-done in virtual mode. That's why we always return whether rm_action is 0 or not when real-mode is enabled. Oh, I misread the code and thought the decision to return was based on the return value of kvmppc_xics_rm_complete. Sorry about that. :-( -Scott -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] KVM: PPC: Book3S: Add support for H_IPOLL and H_XIRR_X in XICS emulation
On Wed, 2013-05-29 at 18:38 -0500, Scott Wood wrote: > > Yes. I'd like to have them in. Their implementation is actually fairly > > trivial and they cannot be emulated by qemu if the rest of the XICS is > > in the kernel, so it's a problem. > > OK. Does it make more sense for you to take it as Paul suggested, or > for Gleb or Marcelo to pick it up directly? I'll take it. > Then rm_action should always be 0 for these hcalls, right? So there's > no correctness reason to keep the hcalls in separate switch > statements. You shave off a few cycles checking rm_action, at the cost > of needing to change kvmppc_xics_hcall() if a real-mode version of > these hcalls is ever done. No, because rm_action will also be 0 if the hcall was fully done in real mode (which can happen, that's our fast path), in which case we do *NOT* want to to be re-done in virtual mode. That's why we always return whether rm_action is 0 or not when real-mode is enabled. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] KVM: PPC: Book3S: Add support for H_IPOLL and H_XIRR_X in XICS emulation
On 05/28/2013 07:41:18 PM, Benjamin Herrenschmidt wrote:
On Tue, 2013-05-28 at 12:41 -0500, Scott Wood wrote:
> I believe Alex is staying far away from e-mail on his vacation.
He's
> asked me to fill in for him while he's gone.
>
> The patch itself seems reasonable (though I don't know much about
XICS,
> and do have one question...), but I'll leave it up to
Gleb/Marcelo/Ben
> if it should go in for 3.10 and via which tree. I understand the
> desire to not have an incomplete ABI in a released version, but
Linus
> is already grumbling about how much went into rc3, and you say the
> hcalls aren't currently used... Are they likely to be used in any
> timeframe in which we'd reasonably care about 3.10?
Yes. I'd like to have them in. Their implementation is actually fairly
trivial and they cannot be emulated by qemu if the rest of the XICS is
in the kernel, so it's a problem.
OK. Does it make more sense for you to take it as Paul suggested, or
for Gleb or Marcelo to pick it up directly?
> > + /* These requests don't have real-mode implementations at
> > present */
> > + switch (req) {
> > + case H_XIRR_X:
> > + res = kvmppc_h_xirr(vcpu);
> > + kvmppc_set_gpr(vcpu, 4, res);
> > + kvmppc_set_gpr(vcpu, 5, get_tb());
> > + return rc;
> > + case H_IPOLL:
> > + rc = kvmppc_h_ipoll(vcpu, kvmppc_get_gpr(vcpu, 4));
> > + return rc;
> > + }
> > +
> > /* Check for real mode returning too hard */
> > if (xics->real_mode)
> > return kvmppc_xics_rm_complete(vcpu, req);
>
> Could you explain what's going on here relative to
> kvmppc_xics_rm_complete()? What does "returning too hard" mean, and
> why must rm_action not be checked for these hcalls?
This is related to how we handle some hcalls in real mode as a fast
path. The real-mode stuff cannot handle cases that require for
example a
re-emit of the interrupt, a reject, etc... so in some cases, it
returns
H_TOO_HARD which causes KVM to exit and try to handle the hcall again
in
kernel virtual mode.
When doing so as the result of a XICS hcall, it sets a bit mask of
"tasks" to handle in virtual mode (because it will have already
partially done the operation, it cannot just re-play the whole hcall).
So when real-mode is supported we must not just call the normal
virtual
mode version of the hcalls, we instead go to kvmppc_xics_rm_complete()
to handle those "tasks".
However, for those 2 "missing" hcalls, we have no real mode
implementation at all (we didn't bother, we will do that later if
needed, it's purely a performance issue). So we need to fully handle
them in virtual mode, and we know there will be no "tasks" to handle
in
rm_complete.
Then rm_action should always be 0 for these hcalls, right? So there's
no correctness reason to keep the hcalls in separate switch
statements. You shave off a few cycles checking rm_action, at the cost
of needing to change kvmppc_xics_hcall() if a real-mode version of
these hcalls is ever done.
-Scott
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Re: [PATCH] KVM: PPC: Book3S: Add support for H_IPOLL and H_XIRR_X in XICS emulation
On Tue, 2013-05-28 at 12:41 -0500, Scott Wood wrote:
> I believe Alex is staying far away from e-mail on his vacation. He's
> asked me to fill in for him while he's gone.
>
> The patch itself seems reasonable (though I don't know much about XICS,
> and do have one question...), but I'll leave it up to Gleb/Marcelo/Ben
> if it should go in for 3.10 and via which tree. I understand the
> desire to not have an incomplete ABI in a released version, but Linus
> is already grumbling about how much went into rc3, and you say the
> hcalls aren't currently used... Are they likely to be used in any
> timeframe in which we'd reasonably care about 3.10?
Yes. I'd like to have them in. Their implementation is actually fairly
trivial and they cannot be emulated by qemu if the rest of the XICS is
in the kernel, so it's a problem.
> If so, would the
> effect of not having them implemented be such that it would be worse
> than not having in-kernel XICS at all?
Well, that would mean that running that potential future kernel that
uses them (or some other OS that already uses them) would not work
without the user explicitly disable in kernel irq chip.
> > @@ -787,6 +804,18 @@ int kvmppc_xics_hcall(struct kvm_vcpu *vcpu, u32
> > req)
> > if (!xics || !vcpu->arch.icp)
> > return H_HARDWARE;
> >
> > + /* These requests don't have real-mode implementations at
> > present */
> > + switch (req) {
> > + case H_XIRR_X:
> > + res = kvmppc_h_xirr(vcpu);
> > + kvmppc_set_gpr(vcpu, 4, res);
> > + kvmppc_set_gpr(vcpu, 5, get_tb());
> > + return rc;
> > + case H_IPOLL:
> > + rc = kvmppc_h_ipoll(vcpu, kvmppc_get_gpr(vcpu, 4));
> > + return rc;
> > + }
> > +
> > /* Check for real mode returning too hard */
> > if (xics->real_mode)
> > return kvmppc_xics_rm_complete(vcpu, req);
>
> Could you explain what's going on here relative to
> kvmppc_xics_rm_complete()? What does "returning too hard" mean, and
> why must rm_action not be checked for these hcalls?
This is related to how we handle some hcalls in real mode as a fast
path. The real-mode stuff cannot handle cases that require for example a
re-emit of the interrupt, a reject, etc... so in some cases, it returns
H_TOO_HARD which causes KVM to exit and try to handle the hcall again in
kernel virtual mode.
When doing so as the result of a XICS hcall, it sets a bit mask of
"tasks" to handle in virtual mode (because it will have already
partially done the operation, it cannot just re-play the whole hcall).
So when real-mode is supported we must not just call the normal virtual
mode version of the hcalls, we instead go to kvmppc_xics_rm_complete()
to handle those "tasks".
However, for those 2 "missing" hcalls, we have no real mode
implementation at all (we didn't bother, we will do that later if
needed, it's purely a performance issue). So we need to fully handle
them in virtual mode, and we know there will be no "tasks" to handle in
rm_complete.
We could have done a real mode variant but we wanted to keep the patch
as small as possible for 3.10.
Cheers,
Ben.
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Re: [PATCH] KVM: PPC: Book3S: Add support for H_IPOLL and H_XIRR_X in XICS emulation
On 05/23/2013 08:42:21 PM, Paul Mackerras wrote:
This adds the remaining two hypercalls defined by PAPR for
manipulating
the XICS interrupt controller, H_IPOLL and H_XIRR_X. H_IPOLL returns
information about the priority and pending interrupts for a virtual
cpu, without changing any state. H_XIRR_X is like H_XIRR in that it
reads and acknowledges the highest-priority pending interrupt, but it
also returns the timestamp (timebase register value) from when the
interrupt was first received by the hypervisor. Currently we just
return the current time, since we don't do any software queueing of
virtual interrupts inside the XICS emulation code.
These hcalls are not currently used by Linux guests, but may be in
future.
Signed-off-by: Paul Mackerras
---
Unfortunately I missed these two hcalls in the previous submissions.
It would be good to get this patch into 3.10 so we don't have a
kernel version with these calls missing from the API, in case future
guest kernels want to use them.
Alex, given you're on vacation at the moment, are you OK with Ben
taking this through his tree?
I believe Alex is staying far away from e-mail on his vacation. He's
asked me to fill in for him while he's gone.
The patch itself seems reasonable (though I don't know much about XICS,
and do have one question...), but I'll leave it up to Gleb/Marcelo/Ben
if it should go in for 3.10 and via which tree. I understand the
desire to not have an incomplete ABI in a released version, but Linus
is already grumbling about how much went into rc3, and you say the
hcalls aren't currently used... Are they likely to be used in any
timeframe in which we'd reasonably care about 3.10? If so, would the
effect of not having them implemented be such that it would be worse
than not having in-kernel XICS at all?
@@ -787,6 +804,18 @@ int kvmppc_xics_hcall(struct kvm_vcpu *vcpu, u32
req)
if (!xics || !vcpu->arch.icp)
return H_HARDWARE;
+ /* These requests don't have real-mode implementations at
present */
+ switch (req) {
+ case H_XIRR_X:
+ res = kvmppc_h_xirr(vcpu);
+ kvmppc_set_gpr(vcpu, 4, res);
+ kvmppc_set_gpr(vcpu, 5, get_tb());
+ return rc;
+ case H_IPOLL:
+ rc = kvmppc_h_ipoll(vcpu, kvmppc_get_gpr(vcpu, 4));
+ return rc;
+ }
+
/* Check for real mode returning too hard */
if (xics->real_mode)
return kvmppc_xics_rm_complete(vcpu, req);
Could you explain what's going on here relative to
kvmppc_xics_rm_complete()? What does "returning too hard" mean, and
why must rm_action not be checked for these hcalls?
-Scott
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