user/sven/linux.git/include/linux/context_tracking.h, branch v5.15.26

context_tracking: KVM: Move guest enter/exit wrappers to KVM's domain

2021-05-05T20:54:12Z

Move the guest enter/exit wrappers to kvm_host.h so that KVM can manage its context tracking vs. vtime accounting without bleeding too many KVM details into the context tracking code. No functional change intended. Signed-off-by: Sean Christopherson Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210505002735.1684165-8-seanjc@google.com

context_tracking: Consolidate guest enter/exit wrappers

2021-05-05T20:54:11Z

Consolidate the guest enter/exit wrappers, providing and tweaking stubs as needed. This will allow moving the wrappers under KVM without having to bleed #ifdefs into the soon-to-be KVM code. No functional change intended. Signed-off-by: Sean Christopherson Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210505002735.1684165-7-seanjc@google.com

sched/vtime: Move guest enter/exit vtime accounting to vtime.h

2021-05-05T20:54:11Z

Provide separate helpers for guest enter vtime accounting (in addition to the existing guest exit helpers), and move all vtime accounting helpers to vtime.h where the existing #ifdef infrastructure can be leveraged to better delineate the different types of accounting. This will also allow future cleanups via deduplication of context tracking code. Opportunstically delete the vtime_account_kernel() stub now that all callers are wrapped with CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y. No functional change intended. Signed-off-by: Sean Christopherson Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210505002735.1684165-6-seanjc@google.com

context_tracking: Move guest exit vtime accounting to separate helpers

2021-05-05T20:54:11Z

Provide separate vtime accounting functions for guest exit instead of open coding the logic within the context tracking code. This will allow KVM x86 to handle vtime accounting slightly differently when using tick-based accounting. Suggested-by: Thomas Gleixner Signed-off-by: Wanpeng Li Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Signed-off-by: Thomas Gleixner Reviewed-by: Christian Borntraeger Link: https://lore.kernel.org/r/20210505002735.1684165-3-seanjc@google.com

context_tracking: Move guest exit context tracking to separate helpers

2021-05-05T20:54:10Z

Provide separate context tracking helpers for guest exit, the standalone helpers will be called separately by KVM x86 in later patches to fix tick-based accounting. Suggested-by: Thomas Gleixner Signed-off-by: Wanpeng Li Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210505002735.1684165-2-seanjc@google.com

context_tracking: Don't implement exception_enter/exit() on CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK

2020-11-19T10:25:42Z

The typical steps with context tracking are: 1) Task runs in userspace 2) Task enters the kernel (syscall/exception/IRQ) 3) Task switches from context tracking state CONTEXT_USER to CONTEXT_KERNEL (user_exit()) 4) Task does stuff in kernel 5) Task switches from context tracking state CONTEXT_KERNEL to CONTEXT_USER (user_enter()) 6) Task exits the kernel If an exception fires between 5) and 6), the pt_regs and the context tracking disagree on the context of the faulted/trapped instruction. CONTEXT_KERNEL must be set before the exception handler, that's unconditional for those handlers that want to be able to call into schedule(), but CONTEXT_USER must be restored when the exception exits whereas pt_regs tells that we are resuming to kernel space. This can't be fixed with storing the context tracking state in a per-cpu or per-task variable since another exception may fire onto the current one and overwrite the saved state. Also the task can schedule. So it has to be stored in a per task stack. This is how exception_enter()/exception_exit() paper over the problem: 5) Task switches from context tracking state CONTEXT_KERNEL to CONTEXT_USER (user_enter()) 5.1) Exception fires 5.2) prev_state = exception_enter() // save CONTEXT_USER to prev_state // and set CONTEXT_KERNEL 5.3) Exception handler 5.4) exception_enter(prev_state) // restore CONTEXT_USER 5.5) Exception resumes 6) Task exits the kernel The condition to live without exception_enter()/exception_exit() is to forbid exceptions and IRQs between 2) and 3) and between 5) and 6), or if any is allowed to trigger, it won't call into context tracking, eg: NMIs, and it won't schedule. These requirements are met by architectures supporting CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK and those can therefore afford not to implement this hack. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20201117151637.259084-3-frederic@kernel.org

compiler.h: Move instrumentation_begin()/end() to new header

2020-07-24T11:56:23Z

Linus pointed out that compiler.h - which is a key header that gets included in every single one of the 28,000+ kernel files during a kernel build - was bloated in: 655389666643: ("vmlinux.lds.h: Create section for protection against instrumentation") Linus noted: > I have pulled this, but do we really want to add this to a header file > that is _so_ core that it gets included for basically every single > file built? > > I don't even see those instrumentation_begin/end() things used > anywhere right now. > > It seems excessive. That 53 lines is maybe not a lot, but it pushed > that header file to over 12kB, and while it's mostly comments, it's > extra IO and parsing basically for _every_ single file compiled in the > kernel. > > For what appears to be absolutely zero upside right now, and I really > don't see why this should be in such a core header file! Move these primitives into a new header: , and include that header in the headers that make use of it. Unfortunately one of these headers is asm-generic/bug.h, which does get included in a lot of places, similarly to compiler.h. So the de-bloating effect isn't as good as we'd like it to be - but at least the interfaces are defined separately. No change to functionality intended. Reported-by: Linus Torvalds Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20200604071921.GA1361070@gmail.com Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Peter Zijlstra

context_tracking: Ensure that the critical path cannot be instrumented

2020-06-11T13:14:36Z

context tracking lacks a few protection mechanisms against instrumentation: - While the core functions are marked NOKPROBE they lack protection against function tracing which is required as the function entry/exit points can be utilized by BPF. - static functions invoked from the protected functions need to be marked as well as they can be instrumented otherwise. - using plain inline allows the compiler to emit traceable and probable functions. Fix this by marking the functions noinstr and converting the plain inlines to __always_inline. The NOKPROBE_SYMBOL() annotations are removed as the .noinstr.text section is already excluded from being probed. Cures the following objtool warnings: vmlinux.o: warning: objtool: enter_from_user_mode()+0x34: call to __context_tracking_exit() leaves .noinstr.text section vmlinux.o: warning: objtool: prepare_exit_to_usermode()+0x29: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: syscall_return_slowpath()+0x29: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: do_syscall_64()+0x7f: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: do_int80_syscall_32()+0x3d: call to __context_tracking_enter() leaves .noinstr.text section vmlinux.o: warning: objtool: do_fast_syscall_32()+0x9c: call to __context_tracking_enter() leaves .noinstr.text section and generates new ones... Signed-off-by: Thomas Gleixner Reviewed-by: Masami Hiramatsu Reviewed-by: Alexandre Chartre Acked-by: Peter Zijlstra Link: https://lkml.kernel.org/r/20200505134340.811520478@linutronix.de

context_tracking: Make guest_enter/exit() .noinstr ready

2020-05-19T13:47:21Z

Force inlining of the helpers and mark the instrumentable parts accordingly. Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Acked-by: Peter Zijlstra Link: https://lkml.kernel.org/r/20200505134341.672545766@linutronix.de

KVM: remove unused guest_enter

2020-01-27T18:59:55Z

After commit 61bd0f66ff92 ("KVM: PPC: Book3S HV: Fix guest time accounting with VIRT_CPU_ACCOUNTING_GEN"), no one use this function anymore, So better to remove it. Signed-off-by: Alex Shi Cc: Paolo Bonzini Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org Signed-off-by: Paolo Bonzini