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Tue, 13 Oct 2026 07:33:15 -0700 (PDT) Received: from pve-server ([49.205.216.49]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3537ca6d20dsm47942824eec.12.2026.10.13.07.33.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 07:33:13 -0700 (PDT) From: Ritesh Harjani (IBM) To: Gautam Menghani , maddy@linux.ibm.com, npiggin@gmail.com, mpe@ellerman.id.au, chleroy@kernel.org, sshegde@linux.ibm.com, amachhiw@linux.ibm.com Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v3 4/4] KVM: PPC: Book3S HV: Take SRCU read lock around kvmppc_h_page_init() call In-Reply-To: <20261012082922.218799-5-gautam@linux.ibm.com> Date: Tue, 13 Oct 2026 20:01:51 +0530 Message-ID: References: <20261012082922.218799-1-gautam@linux.ibm.com> <20261012082922.218799-5-gautam@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Gautam Menghani writes: > Since there is no srcu read lock around kvmppc_h_page_init(), a > "suspicious rcu_dereference_check() usage" can be triggered by running > host linux with CONFIG_PROVE_RCU=y and the following code in the guest: > > plpar_hcall_norets(H_PAGE_INIT, H_ZERO_PAGE, phys_addr, 0); > > ============================= > WARNING: suspicious RCU usage > 7.0.0-dirty #227 Not tainted > ----------------------------- > ./include/linux/kvm_host.h:1074 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > rcu_scheduler_active = 2, debug_locks = 1 > 1 lock held by qemu-system-ppc/2093: > #0: c000000354197ab0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x10c/0xaf0 > > stack backtrace: > CPU: 30 UID: 0 PID: 2093 Comm: qemu-system-ppc Not tainted 7.0.0-dirty #227 PREEMPT(full) > Hardware name: IBM,9080-HEX POWER10 (architected) 0x800200 0xf000006 of:IBM,FW1060.60 (NH1060_158) hv:phyp pSeries > Call Trace: > [c00000033e1bf430] [c000000001b3dbd4] dump_stack_lvl+0xc8/0x130 (unreliable) > [c00000033e1bf470] [c0000000003da964] lockdep_rcu_suspicious+0x1f4/0x290 > [c00000033e1bf520] [c000000000231424] gfn_to_memslot+0x1b4/0x1c0 > [c00000033e1bf560] [c00000000023637c] kvm_clear_guest+0x9c/0x110 > [c00000033e1bf5c0] [c0000000002714a4] kvmppc_h_page_init+0x160/0x1a0 > [c00000033e1bf610] [c00000000026c040] kvmppc_pseries_do_hcall+0x1930/0x1940 > [c00000033e1bf6d0] [c00000000026fb18] kvmppc_vcpu_run_hv+0x268/0x800 > [c00000033e1bf7a0] [c000000000246b30] kvmppc_vcpu_run+0x30/0x50 > [c00000033e1bf7c0] [c000000000241ed4] kvm_arch_vcpu_ioctl_run+0x364/0x530 > [c00000033e1bf860] [c00000000022b870] kvm_vcpu_ioctl+0x1b0/0xaf0 > [c00000033e1bfa50] [c0000000009b4514] sys_ioctl+0x144/0x190 > [c00000033e1bfab0] [c000000000034330] system_call_exception+0x170/0x370 > [c00000033e1bfe50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec > > Fix this by taking a srcu read lock around kvmppc_h_page_init(). Looks good to me. Please feel free to add: Reviewed-by: Ritesh Harjani (IBM)