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Tue, 18 Jan 2022 12:08:33 +0000 (GMT) Received: from [9.171.19.84] (unknown [9.171.19.84]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 18 Jan 2022 12:08:33 +0000 (GMT) Message-ID: <345ed0e0-d33a-3969-3f07-6e4fd3c20775@linux.ibm.com> Date: Tue, 18 Jan 2022 13:08:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH 0/5] kvm: fix latent guest entry/exit bugs Content-Language: en-US To: Mark Rutland , Paolo Bonzini Cc: linux-kernel@vger.kernel.org, aleksandar.qemu.devel@gmail.com, alexandru.elisei@arm.com, anup.patel@wdc.com, aou@eecs.berkeley.edu, atish.patra@wdc.com, benh@kernel.crashing.org, bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org, dave.hansen@linux.intel.com, david@redhat.com, frankja@linux.ibm.com, frederic@kernel.org, gor@linux.ibm.com, hca@linux.ibm.com, imbrenda@linux.ibm.com, james.morse@arm.com, jmattson@google.com, joro@8bytes.org, kvm@vger.kernel.org, maz@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, nsaenzju@redhat.com, palmer@dabbelt.com, paulmck@kernel.org, paulus@samba.org, paul.walmsley@sifive.com, seanjc@google.com, suzuki.poulose@arm.com, tglx@linutronix.de, tsbogend@alpha.franken.de, vkuznets@redhat.com, wanpengli@tencent.com, will@kernel.org References: <20220111153539.2532246-1-mark.rutland@arm.com> <127a6117-85fb-7477-983c-daf09e91349d@linux.ibm.com> <8aa0cada-7f00-47b3-41e4-8a9e7beaae47@redhat.com> <20220118120154.GA17938@C02TD0UTHF1T.local> From: Christian Borntraeger In-Reply-To: <20220118120154.GA17938@C02TD0UTHF1T.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: rIjzolKUCnjTFSyInxWYQVlFrYiJcev_ X-Proofpoint-ORIG-GUID: 9YTZW9Rrm2_i8H2h1CuE4iOxW_hFopZW X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2022-01-18_03,2022-01-18_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 clxscore=1015 lowpriorityscore=0 bulkscore=0 priorityscore=1501 mlxlogscore=999 spamscore=0 phishscore=0 adultscore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2201180074 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Am 18.01.22 um 13:02 schrieb Mark Rutland: > On Mon, Jan 17, 2022 at 06:45:36PM +0100, Paolo Bonzini wrote: >> On 1/14/22 16:19, Mark Rutland wrote: >>> I also think there is another issue here. When an IRQ is taken from SIE, will >>> user_mode(regs) always be false, or could it be true if the guest userspace is >>> running? If it can be true I think tha context tracking checks can complain, >>> and it*might* be possible to trigger a panic(). >> >> I think that it would be false, because the guest PSW is in the SIE block >> and switched on SIE entry and exit, but I might be incorrect. > > Ah; that's the crux of my confusion: I had thought the guest PSW would > be placed in the regular lowcore *_old_psw slots. From looking at the > entry asm it looks like the host PSW (around the invocation of SIE) is > stored there, since that's what the OUTSIDE + SIEEXIT handling is > checking for. Yes, Paolos observation is correct. > > Assuming that's correct, I agree this problem doesn't exist, and there's > only the common RCU/tracing/lockdep management to fix. > > Sorry for the noise, and thanks for the pointer! > > Thanks, > Mark.