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Date: Tue, 23 Jan 2018 19:30:33 +1100
From: Paul Mackerras <paulus@ozlabs.org>
To: wei.guo.simon@gmail.com
Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org
Subject: Re: [PATCH 19/26] KVM: PPC: Book3S PR: always fail transaction in
 guest privilege state
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On Thu, Jan 11, 2018 at 06:11:32PM +0800, wei.guo.simon@gmail.com wrote:
> From: Simon Guo <wei.guo.simon@gmail.com>
> 
> Currently kernel doesn't use transaction memory.
> And there is an issue for privilege guest that:
> tbegin/tsuspend/tresume/tabort TM instructions can impact MSR TM bits
> without trap into PR host. So following code will lead to a false mfmsr
> result:
> 	tbegin	<- MSR bits update to Transaction active.
> 	beq 	<- failover handler branch
> 	mfmsr	<- still read MSR bits from magic page with
> 		transaction inactive.
> 
> It is not an issue for non-privilege guest since its mfmsr is not patched
> with magic page and will always trap into PR host.
> 
> This patch will always fail tbegin attempt for privilege guest, so that
> the above issue is prevented. It is benign since currently (guest) kernel
> doesn't initiate a transaction.
> 
> Test case:
> https://github.com/justdoitqd/publicFiles/blob/master/test_tbegin_pr.c
> 
> Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>

You need to handle the case where MSR_TM is not set in the guest MSR,
and give the guest a facility unavailable interrupt.

[snip]

> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -255,7 +255,7 @@ static inline void kvmppc_save_tm_sprs(struct kvm_vcpu *vcpu)
>  	tm_disable();
>  }
>  
> -static inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu)
> +inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu)

You should probably remove the 'inline' here too.

Paul.