Re: [PATCH v2 18/30] KVM: PPC: Book3S PR: always fail transaction in guest privilege state

Hi Paul,
On Tue, May 15, 2018 at 04:07:55PM +1000, Paul Mackerras wrote:

On Wed, Feb 28, 2018 at 01:52:26AM +0800, wei.guo.simon@gmail.com wrote:

quoted

From: Simon Guo <redacted>

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 <redacted>
---
 arch/powerpc/include/asm/kvm_book3s.h |  2 ++
 arch/powerpc/kvm/book3s_emulate.c     | 43 +++++++++++++++++++++++++++++++++++
 arch/powerpc/kvm/book3s_pr.c          | 11 ++++++++-
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index 2ecb6a3..9690280 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h

@@ -258,9 +258,11 @@ extern void kvmppc_copy_from_svcpu(struct kvm_vcpu *vcpu,
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 void kvmppc_save_tm_pr(struct kvm_vcpu *vcpu);
 void kvmppc_restore_tm_pr(struct kvm_vcpu *vcpu);
+void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu);
 #else
 static inline void kvmppc_save_tm_pr(struct kvm_vcpu *vcpu) {}
 static inline void kvmppc_restore_tm_pr(struct kvm_vcpu *vcpu) {}
+static inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu) {}
 #endif
 
 extern int kvm_irq_bypass;

diff --git a/arch/powerpc/kvm/book3s_emulate.c b/arch/powerpc/kvm/book3s_emulate.c
index a03533d..90b5f59 100644
--- a/arch/powerpc/kvm/book3s_emulate.c
+++ b/arch/powerpc/kvm/book3s_emulate.c

@@ -23,6 +23,7 @@
 #include <asm/reg.h>
 #include <asm/switch_to.h>
 #include <asm/time.h>
+#include <asm/tm.h>
 #include "book3s.h"
 
 #define OP_19_XOP_RFID		18

@@ -47,6 +48,8 @@
 #define OP_31_XOP_EIOIO		854
 #define OP_31_XOP_SLBMFEE	915
 
+#define OP_31_XOP_TBEGIN	654
+
 /* DCBZ is actually 1014, but we patch it to 1010 so we get a trap */
 #define OP_31_XOP_DCBZ		1010
 

@@ -362,6 +365,46 @@ int kvmppc_core_emulate_op_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
 
 			break;
 		}
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+		case OP_31_XOP_TBEGIN:
+		{
+			if (!cpu_has_feature(CPU_FTR_TM))
+				break;
+
+			if (!(kvmppc_get_msr(vcpu) & MSR_TM)) {
+				kvmppc_trigger_fac_interrupt(vcpu, FSCR_TM_LG);
+				emulated = EMULATE_AGAIN;
+				break;
+			}
+
+			if (!(kvmppc_get_msr(vcpu) & MSR_PR)) {
+				preempt_disable();
+				vcpu->arch.cr = (CR0_TBEGIN_FAILURE |
+				  (vcpu->arch.cr & ~(CR0_MASK << CR0_SHIFT)));
+
+				vcpu->arch.texasr = (TEXASR_FS | TEXASR_EX |
+					(((u64)(TM_CAUSE_EMULATE | TM_CAUSE_PERSISTENT))
+						 << TEXASR_FC_LG));
+
+				if ((inst >> 21) & 0x1)
+					vcpu->arch.texasr |= TEXASR_ROT;
+
+				if (kvmppc_get_msr(vcpu) & MSR_PR)
+					vcpu->arch.texasr |= TEXASR_PR;

This if statement seems unnecessary, since we only get here when
MSR_PR is clear.

Yes. I will remove that.

Thanks,
- Simon