Re: [PATCH v5 00/17] KVM nVHE Hypervisor stack unwinder

Kalesh Singh
2022-07-21T16:06:23Z

On Thu, Jul 21, 2022 at 2:56 AM Fuad Tabba <tabba@google.com> wrote:
>
> Hi Kalesh,
>
>
> On Thu, Jul 21, 2022 at 6:57 AM Kalesh Singh <kaleshsingh@google.com> wrote:
> >
> > Hi all,
> >
> > This is v5 of nVHE hypervisor stacktraces support. The series is based on
> > arm64 for-next/stacktrace.
> >
> > The previous versions were posted at:
> > v4: https://lore.kernel.org/r/20220715061027.1612149-1-kaleshsingh@google.com/
> > v3: https://lore.kernel.org/r/20220607165105.639716-1-kaleshsingh@google.com/
> > v2: https://lore.kernel.org/r/20220502191222.4192768-1-kaleshsingh@google.com/
> > v1: https://lore.kernel.org/r/20220427184716.1949239-1-kaleshsingh@google.com/
> >
> > The main updates in this version are some refactoring to move stuff out of
> > stacktrace/nvhe.h (leaving only the unwinder implementation in the header);
> > and fixing the symbolization of the hyp stacktrace when KASLR is enabled;
> > along with the addressing the other minor comments.
> >
> > Patch 18 (KVM: arm64: Dump nVHE hypervisor stack on panic) was also squashed
> > into earlier patches.
> >
> > The previous cover letter is copied below for convenience.
> >
> > Thanks all for your feedback.
>
> Thank you for this. This will be very helpful.
>
> For the whole series:
> Tested-by: Fuad Tabba <tabba@google.com>

Thanks for your reviews, Fuad.

--Kalesh

>
> Cheers,
> /fuad
>
>
> >
> > --Kalesh
> >
> > ============
> >
> > KVM nVHE Stack unwinding.
> > ===
> >
> > nVHE has two modes of operation: protected (pKVM) and unprotected
> > (conventional nVHE). Depending on the mode, a slightly different approach
> > is used to dump the hypervisor stacktrace but the core unwinding logic
> > remains the same.
> >
> > Protected nVHE (pKVM) stacktraces
> > ====
> >
> > In protected nVHE mode, the host cannot directly access hypervisor memory.
> >
> > The hypervisor stack unwinding happens in EL2 and is made accessible to
> > the host via a shared buffer. Symbolizing and printing the stacktrace
> > addresses is delegated to the host and happens in EL1.
> >
> > Non-protected (Conventional) nVHE stacktraces
> > ====
> >
> > In non-protected mode, the host is able to directly access the hypervisor
> > stack pages.
> >
> > The hypervisor stack unwinding and dumping of the stacktrace is performed
> > by the host in EL1, as this avoids the memory overhead of setting up
> > shared buffers between the host and hypervisor.
> >
> > Resuing the Core Unwinding Logic
> > ====
> >
> > Since the hypervisor cannot link against the kernel code in proteced mode.
> > The common stack unwinding code is moved to a shared header to allow reuse
> > in the nVHE hypervisor.
> >
> > Reducing the memory footprint
> > ====
> >
> > In this version the below steps were taken to reduce the memory usage of
> > nVHE stack unwinding:
> >
> > 1) The nVHE overflow stack is reduced from PAGE_SIZE to 4KB; benificial
> > for configurations with non 4KB pages (16KB or 64KB pages).
> > 2) In protected nVHE mode (pKVM), the shared stacktrace buffers with the
> > host are reduced from PAGE_SIZE to the minimum size required.
> > 3) In systems other than Android, conventional nVHE makes up the vast
> > majority of use case. So the pKVM stack tracing is disabled by default
> > (!CONFIG_PROTECTED_NVHE_STACKTRACE), which avoid the memory usage for
> > setting up shared buffers.
> > 4) In non-protected nVHE mode (conventional nVHE), the stack unwinding
> > is done directly in EL1 by the host and no shared buffers with the
> > hypervisor are needed.
> >
> > Sample Output
> > ====
> >
> > The below shows an example output from a simple stack overflow test:
> >
> > [ 126.862960] kvm [371]: nVHE hyp panic at: [<ffff8000090a51d0>] __kvm_nvhe_recursive_death+0x10/0x34!
> > [ 126.869920] kvm [371]: Protected nVHE HYP call trace:
> > [ 126.870528] kvm [371]: [<ffff8000090a5570>] __kvm_nvhe_hyp_panic+0xac/0xf8
> > [ 126.871342] kvm [371]: [<ffff8000090a55cc>] __kvm_nvhe_hyp_panic_bad_stack+0x10/0x10
> > [ 126.872174] kvm [371]: [<ffff8000090a51e4>] __kvm_nvhe_recursive_death+0x24/0x34
> > [ 126.872971] kvm [371]: [<ffff8000090a51e4>] __kvm_nvhe_recursive_death+0x24/0x34
> > . . .
> >
> > [ 126.927314] kvm [371]: [<ffff8000090a51e4>] __kvm_nvhe_recursive_death+0x24/0x34
> > [ 126.927727] kvm [371]: [<ffff8000090a51e4>] __kvm_nvhe_recursive_death+0x24/0x34
> > [ 126.928137] kvm [371]: [<ffff8000090a4de4>] __kvm_nvhe___kvm_vcpu_run+0x30/0x40c
> > [ 126.928561] kvm [371]: [<ffff8000090a7b64>] __kvm_nvhe_handle___kvm_vcpu_run+0x30/0x48
> > [ 126.928984] kvm [371]: [<ffff8000090a78b8>] __kvm_nvhe_handle_trap+0xc4/0x128
> > [ 126.929385] kvm [371]: [<ffff8000090a6864>] __kvm_nvhe___host_exit+0x64/0x64
> > [ 126.929804] kvm [371]: ---- End of Protected nVHE HYP call trace ----
> >
> > ============
> >
> > Kalesh Singh (17):
> > arm64: stacktrace: Add shared header for common stack unwinding code
> > arm64: stacktrace: Factor out on_accessible_stack_common()
> > arm64: stacktrace: Factor out unwind_next_common()
> > arm64: stacktrace: Handle frame pointer from different address spaces
> > arm64: stacktrace: Factor out common unwind()
> > arm64: stacktrace: Add description of stacktrace/common.h
> > KVM: arm64: On stack overflow switch to hyp overflow_stack
> > KVM: arm64: Add PROTECTED_NVHE_STACKTRACE Kconfig
> > KVM: arm64: Allocate shared pKVM hyp stacktrace buffers
> > KVM: arm64: Stub implementation of pKVM HYP stack unwinder
> > KVM: arm64: Stub implementation of non-protected nVHE HYP stack
> > unwinder
> > KVM: arm64: Save protected-nVHE (pKVM) hyp stacktrace
> > KVM: arm64: Prepare non-protected nVHE hypervisor stacktrace
> > KVM: arm64: Implement protected nVHE hyp stack unwinder
> > KVM: arm64: Implement non-protected nVHE hyp stack unwinder
> > KVM: arm64: Introduce pkvm_dump_backtrace()
> > KVM: arm64: Introduce hyp_dump_backtrace()
> >
> > arch/arm64/include/asm/kvm_asm.h | 16 ++
> > arch/arm64/include/asm/memory.h | 8 +
> > arch/arm64/include/asm/stacktrace.h | 92 +++++----
> > arch/arm64/include/asm/stacktrace/common.h | 230 +++++++++++++++++++++
> > arch/arm64/include/asm/stacktrace/nvhe.h | 199 ++++++++++++++++++
> > arch/arm64/kernel/stacktrace.c | 157 --------------
> > arch/arm64/kvm/Kconfig | 15 ++
> > arch/arm64/kvm/arm.c | 2 +-
> > arch/arm64/kvm/handle_exit.c | 101 +++++++++
> > arch/arm64/kvm/hyp/nvhe/Makefile | 2 +-
> > arch/arm64/kvm/hyp/nvhe/host.S | 9 +-
> > arch/arm64/kvm/hyp/nvhe/stacktrace.c | 116 +++++++++++
> > arch/arm64/kvm/hyp/nvhe/switch.c | 6 +
> > 13 files changed, 749 insertions(+), 204 deletions(-)
> > create mode 100644 arch/arm64/include/asm/stacktrace/common.h
> > create mode 100644 arch/arm64/include/asm/stacktrace/nvhe.h
> > create mode 100644 arch/arm64/kvm/hyp/nvhe/stacktrace.c
> >
> >
> > base-commit: 82a592c13b0aeff94d84d54183dae0b26384c95f
> > --
> > 2.37.0.170.g444d1eabd0-goog
> >