diff mbox series

[v4,09/46] powerpc/64s: remove KVM SKIP test from instruction breakpoint handler

Message ID 20210323010305.1045293-10-npiggin@gmail.com
State New
Headers show
Series KVM: PPC: Book3S: C-ify the P9 entry/exit code | expand

Commit Message

Nicholas Piggin March 23, 2021, 1:02 a.m. UTC 
The code being executed in KVM_GUEST_MODE_SKIP is hypervisor code with
MSR[IR]=0, so the faults of concern are the d-side ones caused by access
to guest context by the hypervisor.

Instruction breakpoint interrupts are not a concern here. It's unlikely
any good would come of causing breaks in this code, but skipping the
instruction that caused it won't help matters (e.g., skip the mtmsr that
sets MSR[DR]=0 or clears KVM_GUEST_MODE_SKIP).

Reviewed-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 1 -
 1 file changed, 1 deletion(-)

Comments

Paul Mackerras March 31, 2021, 4:54 a.m. UTC | #1 
On Tue, Mar 23, 2021 at 11:02:28AM +1000, Nicholas Piggin wrote:
> The code being executed in KVM_GUEST_MODE_SKIP is hypervisor code with
> MSR[IR]=0, so the faults of concern are the d-side ones caused by access
> to guest context by the hypervisor.
> 
> Instruction breakpoint interrupts are not a concern here. It's unlikely
> any good would come of causing breaks in this code, but skipping the
> instruction that caused it won't help matters (e.g., skip the mtmsr that
> sets MSR[DR]=0 or clears KVM_GUEST_MODE_SKIP).
> 
> Reviewed-by: Daniel Axtens <dja@axtens.net>
> Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

It might be worth noting in the commit message that the 0x1300
interrupt was dropped from the architecture a long time ago and is not
generated by P7, P8, P9 or P10.

Acked-by: Paul Mackerras <paulus@ozlabs.org>
Nicholas Piggin April 1, 2021, 9:47 a.m. UTC | #2 
Excerpts from Paul Mackerras's message of March 31, 2021 2:54 pm:
> On Tue, Mar 23, 2021 at 11:02:28AM +1000, Nicholas Piggin wrote:
>> The code being executed in KVM_GUEST_MODE_SKIP is hypervisor code with
>> MSR[IR]=0, so the faults of concern are the d-side ones caused by access
>> to guest context by the hypervisor.
>> 
>> Instruction breakpoint interrupts are not a concern here. It's unlikely
>> any good would come of causing breaks in this code, but skipping the
>> instruction that caused it won't help matters (e.g., skip the mtmsr that
>> sets MSR[DR]=0 or clears KVM_GUEST_MODE_SKIP).
>> 
>> Reviewed-by: Daniel Axtens <dja@axtens.net>
>> Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> 
> It might be worth noting in the commit message that the 0x1300
> interrupt was dropped from the architecture a long time ago and is not
> generated by P7, P8, P9 or P10.

Good background, I'll add that.

Thanks,
Nick

> 
> Acked-by: Paul Mackerras <paulus@ozlabs.org>
>
diff mbox series

Patch

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index a0515cb829c2..c9c446ccff54 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -2553,7 +2553,6 @@  EXC_VIRT_NONE(0x5200, 0x100)
 INT_DEFINE_BEGIN(instruction_breakpoint)
 	IVEC=0x1300
 #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
-	IKVM_SKIP=1
 	IKVM_REAL=1
 #endif
 INT_DEFINE_END(instruction_breakpoint)