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Mon, 12 Oct 2026 08:12:54 +0000 (GMT) Received: from osiris (unknown [9.224.76.185]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTPS; Mon, 12 Oct 2026 08:12:54 +0000 (GMT) Date: Mon, 12 Oct 2026 10:12:54 +0200 From: Steffen Eiden To: Kristina =?utf-8?Q?Mart=C5=A1enko?= Cc: linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, kvmarm@lists.linux.dev, linux-efi@vger.kernel.org, Catalin Marinas , Will Deacon , Mark Rutland , Ryan Roberts , David Hildenbrand , Lorenzo Stoakes , Linu Cherian , Anshuman Khandual , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Marc Zyngier , Oliver Upton , Fuad Tabba , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Ard Biesheuvel , Ilias Apalodimas Subject: Re: [RFC 03/12] KVM: arm64: Hide TLBID from guest sysregs Message-ID: <20261012081254.483793-A-seiden@linux.ibm.com> References: <20261001110655.461473-1-kristina.martsenko@arm.com> <20261001110655.461473-4-kristina.martsenko@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261001110655.461473-4-kristina.martsenko@arm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDEyMDAzMCBTYWx0ZWRfXwppdWWnupKZm R5YMszWuISLyqitb5l6P4CFHM1PSLZbI2vFgULl0Ezon7SDFxNi6TtsKy/2QF+EgiKDaanozKpV riftcLPbkcFymJV/YWaHqI6e6+8vxbM60twnDLkkevRDaR+xi9rhVwUxizMtS4XvYNNpDoKdTeB ZVF3lydm8vAwBBLOyL09b6gDa9sgidnka7ZchMinvuyuKKduJQd/InGs1zbj1fRjHKlfYA77b5J ezd2Eo5WUQO3n7uSSw10zHmhmG4PMqHW1vJo+UiqWDjAzRVjn9t+Dx/d9uOVdaOFTQkpeRZLUr9 iFhaOLwmGpPNu711xbvelXxryzFOBe43mMrRJHJ8EAXirMGUWWpZ6Hmjw3qJ1sGBdxaC33yZDlV gtbT/LyTGpA7sZdEG8cD0Zsd2WmBUk70d2RbRMylEmUGcgQagN2pYpxi8wtfIQQmUtEjO1V/SSD Llpdp2aEjhwLkgpu9Wg== X-Proofpoint-GUID: 8WRxpz4LaIopRuMISbZzH7WHNCyEDW2E X-Proofpoint-ORIG-GUID: 8WRxpz4LaIopRuMISbZzH7WHNCyEDW2E X-Proofpoint-Spam-Info: AW1haW4tMjYxMDEyMDAzMCBTYWx0ZWRfXxbNOPlqJaejr VwcYq80OnPhGOgQVe5J3o4GitrvU6jbbx4zmHB3S1PzoX3pEh6kHjUEe2Dr6yCsnfEC3JA/w8LD wIRGEC2vLHyRR58cGJZJ5aTVymA06Zc= X-Authority-Analysis: v=2.4 cv=btHZl0ai c=1 sm=1 tr=0 ts=6acc9689 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=9Dg5do3rMOcXWvYwyOwA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-10-12_02,2026-10-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 malwarescore=0 phishscore=0 impostorscore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 clxscore=1011 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610080000 definitions=main-2610120030 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261012_011313_463628_3462E37E X-CRM114-Status: GOOD ( 17.78 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 01, 2026 at 12:06:46PM +0100, Kristina Martšenko wrote: > Don't expose FEAT_TLBID to guests. It wouldn't be useful in the general > case since a guest doesn't know which domains exist and its vCPUs can be > moved between any physical CPUs. > > Try to hide TLBID sysregs and sysreg fields from the guest: > > * Report the feature as not supported in the ID register > ID_AA64MMFR4_EL1.TLBID. > > * Configure the TLBIDIDR_EL1 sysreg to UNDEF via the FGU mechanism. > Sanitize a nested hypervisor's HFGRTR2.nTLBIDIDR. > > * Sanitize a nested hypervisor's HCRX.{VTLBIDEn,VTLBIDOSEn,FNB}. > > * VTLBID{OS}_EL2 registers are VNCR-backed and not exposed to > guests (apart from being able to read/write into the VNCR page) so > no need to handle them in sys_reg_descs or elsewhere. > > * The guest is free to set SCTLR2_EL{1,2}.TLBOSNIS, which shouldn't > matter to KVM. > What confuse me where a bit that you wrote 'try to hide'. For me this indicates that the hiding process may not be successful. For me the code looks like it will always succeddin hiding the feature from the guest, no? Did I miss anything? Same for the next patch. Steffen