From: Nicholas Piggin <npiggin@gmail.com>
To: Fabiano Rosas <farosas@linux.ibm.com>, kvm-ppc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v1 01/12] KVM: PPC: Book3S HV P9: Restore host CTRL SPR after guest exit
Date: Tue, 13 Apr 2021 11:25:51 +1000 [thread overview]
Message-ID: <1618276972.38i1q7a28t.astroid@bobo.none> (raw)
In-Reply-To: <877dl761iv.fsf@linux.ibm.com>
Excerpts from Fabiano Rosas's message of April 13, 2021 12:06 am:
> Nicholas Piggin <npiggin@gmail.com> writes:
>
>> The host CTRL (runlatch) value is not restored after guest exit. The
>> host CTRL should always be 1 except in CPU idle code, so this can result
>> in the host running with runlatch clear, and potentially switching to
>> a different vCPU which then runs with runlatch clear as well.
>>
>> This has little effect on P9 machines, CTRL is only responsible for some
>> PMU counter logic in the host and so other than corner cases of software
>> relying on that, or explicitly reading the runlatch value (Linux does
>> not appear to be affected but it's possible non-Linux guests could be),
>> there should be no execution correctness problem, though it could be
>> used as a covert channel between guests.
>>
>> There may be microcontrollers, firmware or monitoring tools that sample
>> the runlatch value out-of-band, however since the register is writable
>> by guests, these values would (should) not be relied upon for correct
>> operation of the host, so suboptimal performance or incorrect reporting
>> should be the worst problem.
>>
>> Fixes: 95a6432ce9038 ("KVM: PPC: Book3S HV: Streamlined guest entry/exit path on P9 for radix guests")
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>> arch/powerpc/kvm/book3s_hv.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index 13bad6bf4c95..208a053c9adf 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -3728,7 +3728,10 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
>> vcpu->arch.dec_expires = dec + tb;
>> vcpu->cpu = -1;
>> vcpu->arch.thread_cpu = -1;
>> + /* Save guest CTRL register, set runlatch to 1 */
>> vcpu->arch.ctrl = mfspr(SPRN_CTRLF);
>> + if (!(vcpu->arch.ctrl & 1))
>> + mtspr(SPRN_CTRLT, vcpu->arch.ctrl | 1);
>
> Maybe ditch the comment and use the already defined CTRL_RUNLATCH?
I did it this way so you can more easily match up the C with the
existing asm version.
I have a later patch to clean up CTRL handling a bit (in both C and
asm).
Thanks,
Nick
next prev parent reply other threads:[~2021-04-13 1:26 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-12 1:48 [PATCH v1 00/12] minor KVM fixes and cleanups Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 01/12] KVM: PPC: Book3S HV P9: Restore host CTRL SPR after guest exit Nicholas Piggin
2021-04-12 14:06 ` Fabiano Rosas
2021-04-13 1:25 ` Nicholas Piggin [this message]
2021-04-12 1:48 ` [PATCH v1 02/12] KVM: PPC: Book3S HV: Nested move LPCR sanitising to sanitise_hv_regs Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 03/12] KVM: PPC: Book3S HV: Add a function to filter guest LPCR bits Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 04/12] KVM: PPC: Book3S HV: Disallow LPCR[AIL] to be set to 1 or 2 Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 05/12] KVM: PPC: Book3S HV: Prevent radix guests setting LPCR[TC] Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 06/12] KVM: PPC: Book3S HV: Remove redundant mtspr PSPB Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 07/12] KVM: PPC: Book3S HV: remove unused kvmppc_h_protect argument Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 08/12] KVM: PPC: Book3S HV: Fix CONFIG_SPAPR_TCE_IOMMU=n default hcalls Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 09/12] powerpc/64s: Remove KVM handler support from CBE_RAS interrupts Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 10/12] powerpc/64s: remove KVM SKIP test from instruction breakpoint handler Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 11/12] KVM: PPC: Book3S HV: Ensure MSR[ME] is always set in guest MSR Nicholas Piggin
2021-04-12 1:48 ` [PATCH v1 12/12] KVM: PPC: Book3S HV: Ensure MSR[HV] is always clear " Nicholas Piggin
2021-04-16 18:34 ` Fabiano Rosas
2021-04-19 3:59 ` [PATCH v1 00/12] minor KVM fixes and cleanups Michael Ellerman
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