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Date:   Thu, 20 Jan 2022 12:28:09 +0100
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Subject: Re: [PATCH v2 0/7] kvm: fix latent guest entry/exit bugs
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To:     Mark Rutland <mark.rutland@arm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        aleksandar.qemu.devel@gmail.com, alexandru.elisei@arm.com,
        anup.patel@wdc.com, aou@eecs.berkeley.edu, atish.patra@wdc.com,
        bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org,
        dave.hansen@linux.intel.com, frankja@linux.ibm.com,
        frederic@kernel.org, gor@linux.ibm.com, hca@linux.ibm.com,
        james.morse@arm.com, jmattson@google.com, joro@8bytes.org,
        luto@kernel.org, maz@kernel.org, mingo@redhat.com,
        nsaenzju@redhat.com, palmer@dabbelt.com, paulmck@kernel.org,
        paul.walmsley@sifive.com, peterz@infradead.org, seanjc@google.com,
        suzuki.poulose@arm.com, svens@linux.ibm.com, tglx@linutronix.de,
        tsbogend@alpha.franken.de, vkuznets@redhat.com,
        wanpengli@tencent.com, will@kernel.org,
        Anup Patel <anup@brainfault.org>,
        Atish Patra <atishp@atishpatra.org>
References: <20220119105854.3160683-1-mark.rutland@arm.com>
 <a4a26805-3a56-d264-0a7e-60bed1ada9f3@linux.ibm.com>
 <20220119192217.GD43919@C02TD0UTHF1T.local>
From:   Paolo Bonzini <pbonzini@redhat.com>
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On 1/19/22 20:22, Mark Rutland wrote:
> I wonder, is the s390 guest entry/exit*preemptible*  ?
> 
> If a timer IRQ can preempt in the middle of the EQS, we wouldn't balance
> things before a ctx-switch to the idle thread, which would then be able
> to hit this.
> 
> I'll need to go audit the other architectures for similar.

They don't enable interrupts in the entry/exit path so they should be 
okay.  RISC-V and x86 have an explicit preempt_disable/enable, while 
MIPS only has local_irq_disable/enable.

(MIPS is a mess of dead code, I have patches to clean it up).

Paolo