Commit 46a704f8 authored Jun 15, 2017 by Paul Mackerras

KVM: PPC: Book3S HV: Preserve userspace HTM state properly



If userspace attempts to call the KVM_RUN ioctl when it has hardware
transactional memory (HTM) enabled, the values that it has put in the
HTM-related SPRs TFHAR, TFIAR and TEXASR will get overwritten by
guest values.  To fix this, we detect this condition and save those
SPR values in the thread struct, and disable HTM for the task.  If
userspace goes to access those SPRs or the HTM facility in future,
a TM-unavailable interrupt will occur and the handler will reload
those SPRs and re-enable HTM.

If userspace has started a transaction and suspended it, we would
currently lose the transactional state in the guest entry path and
would almost certainly get a "TM Bad Thing" interrupt, which would
cause the host to crash.  To avoid this, we detect this case and
return from the KVM_RUN ioctl with an EINVAL error, with the KVM
exit reason set to KVM_EXIT_FAIL_ENTRY.

Fixes: b005255e ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08)
Cc: stable@vger.kernel.org # v3.14+
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

parent 4c3bb4cc

arch/powerpc/kvm/book3s_hv.c

+21 −0

Original line number	Diff line number	Diff line
		@@ -2916,6 +2916,27 @@ static int kvmppc_vcpu_run_hv(struct kvm_run run, struct kvm_vcpu vcpu)
		return -EINVAL;
		}

		/*
		* Don't allow entry with a suspended transaction, because
		* the guest entry/exit code will lose it.
		* If the guest has TM enabled, save away their TM-related SPRs
		* (they will get restored by the TM unavailable interrupt).
		*/
		#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
		if (cpu_has_feature(CPU_FTR_TM) && current->thread.regs &&
		(current->thread.regs->msr & MSR_TM)) {
		if (MSR_TM_ACTIVE(current->thread.regs->msr)) {
		run->exit_reason = KVM_EXIT_FAIL_ENTRY;
		run->fail_entry.hardware_entry_failure_reason = 0;
		return -EINVAL;
		}
		current->thread.tm_tfhar = mfspr(SPRN_TFHAR);
		current->thread.tm_tfiar = mfspr(SPRN_TFIAR);
		current->thread.tm_texasr = mfspr(SPRN_TEXASR);
		current->thread.regs->msr &= ~MSR_TM;
		}
		#endif

		kvmppc_core_prepare_to_enter(vcpu);

		/* No need to go into the guest when all we'll do is come back out */

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