On 05/09/2013 07:21 PM, Bhushan Bharat-R65777 wrote:
-----Original Message-----
From: tiejun.chen [mailto:tiejun.c...@windriver.com]
Sent: Thursday, May 09, 2013 3:48 PM
To: Bhushan Bharat-R65777
Cc: Caraman Mihai Claudiu-B02008; Wood Scott-B07421; linuxppc-
d...@lists.ozlabs.org; ag...@suse.de; kvm-...@vger.kernel.org;
k...@vger.kernel.org
Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts
On 05/09/2013 06:00 PM, Bhushan Bharat-R65777 wrote:
-----Original Message-----
From: tiejun.chen [mailto:tiejun.c...@windriver.com]
Sent: Thursday, May 09, 2013 3:15 PM
To: Bhushan Bharat-R65777
Cc: Caraman Mihai Claudiu-B02008; Wood Scott-B07421; linuxppc-
d...@lists.ozlabs.org; ag...@suse.de; kvm-...@vger.kernel.org;
k...@vger.kernel.org
Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable
interrupts
On 05/09/2013 04:23 PM, Bhushan Bharat-R65777 wrote:
-----Original Message-----
From: Linuxppc-dev [mailto:linuxppc-dev-
bounces+bharat.bhushan=freescale....@lists.ozlabs.org] On Behalf Of
bounces+Caraman
Mihai Claudiu-B02008
Sent: Wednesday, May 08, 2013 6:44 PM
To: Wood Scott-B07421; tiejun.chen
Cc: linuxppc-dev@lists.ozlabs.org; ag...@suse.de;
kvm-...@vger.kernel.org; k...@vger.kernel.org
Subject: RE: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable
interrupts
This only disable soft interrupt for kvmppc_restart_interrupt()
that restarts interrupts if they were meant for the host:
a. SOFT_DISABLE_INTS() only for BOOKE_INTERRUPT_EXTERNAL |
BOOKE_INTERRUPT_DECREMENTER | BOOKE_INTERRUPT_DOORBELL
Those aren't the only exceptions that can end up going to the host.
We could get a TLB miss that results in a heavyweight MMIO exit, etc.
And shouldn't we handle kvmppc_restart_interrupt() like the
original HOST flow?
#define MASKABLE_EXCEPTION(trapnum, intnum, label, hdlr,
ack) \
START_EXCEPTION(label); \
NORMAL_EXCEPTION_PROLOG(trapnum, intnum,
PROLOG_ADDITION_MASKABLE)\
EXCEPTION_COMMON(trapnum, PACA_EXGEN,
*INTS_DISABLE*) \
...
Could you elaborate on what you mean?
I think Tiejun was saying that host has flags and replays only
EE/DEC/DBELL interrupts. There is special macro
masked_interrupt_book3e in those exception handlers that sets paca-
irq_happened.
The list of replied interrupts is limited to asynchronous
noncritical interrupts which can be masked by MSR[EE] (therefore no TLB
miss).
Now on KVM book3e we don't want to put them in the irq_happened
lazy state but rather to execute them directly, so there is no
reason for exception handling symmetry between host and guest.
Another Question:
The case is:
Actually in the case GS=1 even if EE=0, EXT/DEC/DBELL still occur as I
recall.
Case 1)
-> Local_irq_disable() will set soft_enabled = 0
-> Now Externel interrupt happens, there we set PACA_IRQ_EE in
irq_happened,
Also clears EE in SRR1 and rfi. So interrupts are hard disabled. No
more other interrupt gated by MSR.EE can happen. Looks like the idea
here is to not let a device keep on inserting interrupt till the
interrupt condition on device is cleared, right?
I don't understand "the interrupt condition on device is cleared" here.
I think regardless if you clear the device interrupt status, the
system still receive a pending interrupt once EE or GS = 1.
Once yes, but I think to avoid flood of device interrupt we disable MSR.EE
when soft-disabled.
But we neither ACK nor send EOI to that irq in the interrupt controller, so that
should be in pending state.
-> local_irq_enable() - This checks that irq_happened is set, and
replays
ret_from_except also check to replay.
Now the case 2)
Case 2)
-> Local_irq_disable() will set soft_enabled = 0
-> Now DEC interrupt happens. We set PACA_IRQ_DEC in
irq_happened, But do
not clear EE in SRR1 and rfi. So interrupts are not hard disabled.
-> Now say EE interrupt happens, there we set PACA_IRQ_EE in
irq_happened,
Also clears EE in SRR1 and rfi. So interrupts are hard disabled.
-> local_irq_enable() - This checks that irq_happened is set.
IIUC, it replays only one interrupt? is not it?
After anyone is replayed in arch_local_irq_restore(), we will set
soft/hard interrupt there:
set_soft_enabled(1);
__hard_irq_enable();
Then any pending interrupt can be executed now.
Do you mean that the interrupt should fire again?
I means the pending exception including external interrupt, the decrementer
exception and the doorbell exception, can trap CPU once EE=1 with
__hard_irq_enable() here. Then the kernel can handle those exception since soft
enable is also 1 now.
Additionally, ret_from_except probably check to replay all.
Local_irq_enable() will not take us to ret_from_except.
Yes. I just say ret_from_except can provide an approach to replay all :)
__replay_interrupt() from arch_local_irq_enable() will take us to
ret_from_except/lite :)
There all pending interrupts are replayed one by one before we hard-enable and
soft-enable interrupts.
Yes, but a point needs to be corrected,
_replay_interrupt() is following set_soft_enabled(1), so __replay_interrupt()
can go the exception entry to call the handler.
Tiejun
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