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1508c22f11
The kvm_vcpu_read_guest/kvm_vcpu_write_guest used for nested guests eventually call srcu_dereference_check to dereference a memslot and lockdep produces a warning as neither kvm->slots_lock nor kvm->srcu lock is held and kvm->users_count is above zero (>100 in fact). This wraps mentioned VCPU read/write helpers in srcu read lock/unlock as it is done in other places. This uses vcpu->srcu_idx when possible. These helpers are only used for nested KVM so this may explain why we did not see these before. Here is an example of a warning: ============================= WARNING: suspicious RCU usage 5.7.0-rc3-le_dma-bypass.3.2_a+fstn1 #897 Not tainted ----------------------------- include/linux/kvm_host.h:633 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/2752: #0: c000200359016be0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x144/0xd80 [kvm] stack backtrace: CPU: 80 PID: 2752 Comm: qemu-system-ppc Not tainted 5.7.0-rc3-le_dma-bypass.3.2_a+fstn1 #897 Call Trace: [c0002003591ab240] [c000000000b23ab4] dump_stack+0x190/0x25c (unreliable) [c0002003591ab2b0] [c00000000023f954] lockdep_rcu_suspicious+0x140/0x164 [c0002003591ab330] [c008000004a445f8] kvm_vcpu_gfn_to_memslot+0x4c0/0x510 [kvm] [c0002003591ab3a0] [c008000004a44c18] kvm_vcpu_read_guest+0xa0/0x180 [kvm] [c0002003591ab410] [c008000004ff9bd8] kvmhv_enter_nested_guest+0x90/0xb80 [kvm_hv] [c0002003591ab980] [c008000004fe07bc] kvmppc_pseries_do_hcall+0x7b4/0x1c30 [kvm_hv] [c0002003591aba10] [c008000004fe5d30] kvmppc_vcpu_run_hv+0x10a8/0x1a30 [kvm_hv] [c0002003591abae0] [c008000004a5d954] kvmppc_vcpu_run+0x4c/0x70 [kvm] [c0002003591abb10] [c008000004a56e54] kvm_arch_vcpu_ioctl_run+0x56c/0x7c0 [kvm] [c0002003591abba0] [c008000004a3ddc4] kvm_vcpu_ioctl+0x4ac/0xd80 [kvm] [c0002003591abd20] [c0000000006ebb58] ksys_ioctl+0x188/0x210 [c0002003591abd70] [c0000000006ebc28] sys_ioctl+0x48/0xb0 [c0002003591abdb0] [c000000000042764] system_call_exception+0x1d4/0x2e0 [c0002003591abe20] [c00000000000cce8] system_call_common+0xe8/0x214 Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Signed-off-by: Paul Mackerras <paulus@ozlabs.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.