Re: [PATCH v3 4/4] KVM: PPC: Book3S HV: Take SRCU read lock around kvmppc_h_page_init() call
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From: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Date: 2026-10-13 14:33:16
Also in:
kvm, lkml, stable
Gautam Menghani [off-list ref] 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) <ritesh.list@gmail.com>