Am 13.10.2011 um 07:40 schrieb Bharat Bhushan <r65777@xxxxxxxxxxxxx>:
> The current implementation of mtmsr and mtmsrd are racy in that it does:
>
> * check (int_pending == 0)
> ---> host sets int_pending = 1 <---
> * write shared page
> * done
>
> while instead we should check for int_pending after the shared page is written.
>
> Signed-off-by: Bharat Bhushan <bharat.bhushan@xxxxxxxxxxxxx>
> ---
> arch/powerpc/kernel/kvm_emul.S | 22 ++++++++++------------
> 1 files changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kvm_emul.S b/arch/powerpc/kernel/kvm_emul.S
> index f2b1b25..65f853b 100644
> --- a/arch/powerpc/kernel/kvm_emul.S
> +++ b/arch/powerpc/kernel/kvm_emul.S
> @@ -85,15 +85,15 @@ kvm_emulate_mtmsrd_reg:
> /* Put MSR back into magic page */
> STL64(r31, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
>
> + /* Check if we may trigger an interrupt */
> + andi. r30, r30, MSR_EE
> + beq no_check
> +
> /* Check if we have to fetch an interrupt */
> lwz r31, (KVM_MAGIC_PAGE + KVM_MAGIC_INT)(0)
> cmpwi r31, 0
> beq+ no_check
>
> - /* Check if we may trigger an interrupt */
> - andi. r30, r30, MSR_EE
> - beq no_check
> -
This chunk should actually be ok already. We're basically doing:
if(likely(!int_pending) && !(new_msr & MSR_EE))
goto no_check;
Since we wrote shared.msr before the check, we're good, no?
> SCRATCH_RESTORE
>
> /* Nag hypervisor */
> @@ -167,22 +167,20 @@ maybe_stay_in_guest:
> kvm_emulate_mtmsr_reg2:
> ori r30, r0, 0
>
> - /* Check if we have to fetch an interrupt */
> - lwz r31, (KVM_MAGIC_PAGE + KVM_MAGIC_INT)(0)
> - cmpwi r31, 0
> - beq+ no_mtmsr
> + /* Put MSR into magic page because we don't call mtmsr */
> + STL64(r30, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
>
> /* Check if we may trigger an interrupt */
> andi. r31, r30, MSR_EE
> beq no_mtmsr
>
> - b do_mtmsr
> + /* Check if we have to fetch an interrupt */
> + lwz r31, (KVM_MAGIC_PAGE + KVM_MAGIC_INT)(0)
> + cmpwi r31, 0
> + bne- do_mtmsr
>
> no_mtmsr:
>
> - /* Put MSR into magic page because we don't call mtmsr */
> - STL64(r30, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
> -
This one looks good.
Alex
> SCRATCH_RESTORE
>
> /* Go back to caller */
> --
> 1.7.0.4
>
>
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