Re: [PATCH v4 00/18] KVM nVHE Hypervisor stack unwinder

[Kalesh Singh <kaleshsingh@google.com>]

On Fri, Jul 15, 2022 at 6:55 AM 'Fuad Tabba' via kernel-team
<kernel-team@android.com> wrote:
>
> Hi Kalesh,
>
> On Fri, Jul 15, 2022 at 7:10 AM Kalesh Singh <kaleshsingh@google.com> wrote:
> >
> > Hi all,
> >
> > This is v4 of the series adding support for nVHE hypervisor stacktraces;
> > and is based on arm64 for-next/stacktrace.
> >
> > Thanks all for your feedback on previous revisions. Mark Brown, I
> > appreciate your Reviewed-by on the v3, I have dropped the tags in this
> > new verision since I think the series has changed quite a bit.
> >
> > The previous versions were posted at:
> > 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 to address concerens from Marc on the
> > memory usage and reusing the common code by refactoring into a shared header.
> >
> > Thanks,
> > Kalesh
>
> I tested an earlier version of this patch series, and it worked fine,
> with symbolization. However, testing it now, both with nvhe and with
> pkvm the symbolization isn't working for me. e.g.
>
> [   32.986706] kvm [251]: Protected nVHE HYP call trace:
> [   32.986796] kvm [251]:  [<ffff800008f8b0e0>] 0xffff800008f8b0e0
> [   32.987391] kvm [251]:  [<ffff800008f8b388>] 0xffff800008f8b388
> [   32.987493] kvm [251]:  [<ffff800008f8d230>] 0xffff800008f8d230
> [   32.987591] kvm [251]:  [<ffff800008f8d51c>] 0xffff800008f8d51c
> [   32.987695] kvm [251]:  [<ffff800008f8c064>] 0xffff800008f8c064
> [   32.987803] kvm [251]: ---- End of Protected nVHE HYP call trace ----
>
> CONFIG_PROTECTED_NVHE_STACKTRACE CONFIG_NVHE_EL2_DEBUG and
> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT are all enabled. Generating
> a backtrace in the host I get proper symbolisation.
>
> Is there anything else you'd like to know about my setup that would
> help get to the bottom of this?

Hi Fuad,

Thanks for reviewing it. Can you attach the .config when you have a
chance please? I will try reproducing it on my end.

--Kalesh

>
> Thanks,
> /fuad
>
>
>
>
> >
> > ============
> >
> > 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 hyperviosr 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
> >        hyperviosr 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 (18):
> >   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()
> >   KVM: arm64: Dump nVHE hypervisor stack on panic
> >
> >  arch/arm64/include/asm/kvm_asm.h           |  16 ++
> >  arch/arm64/include/asm/memory.h            |   7 +
> >  arch/arm64/include/asm/stacktrace.h        |  92 ++++---
> >  arch/arm64/include/asm/stacktrace/common.h | 224 ++++++++++++++++
> >  arch/arm64/include/asm/stacktrace/nvhe.h   | 291 +++++++++++++++++++++
> >  arch/arm64/kernel/stacktrace.c             | 157 -----------
> >  arch/arm64/kvm/Kconfig                     |  15 ++
> >  arch/arm64/kvm/arm.c                       |   2 +-
> >  arch/arm64/kvm/handle_exit.c               |   4 +
> >  arch/arm64/kvm/hyp/nvhe/Makefile           |   2 +-
> >  arch/arm64/kvm/hyp/nvhe/host.S             |   9 +-
> >  arch/arm64/kvm/hyp/nvhe/stacktrace.c       | 108 ++++++++
> >  arch/arm64/kvm/hyp/nvhe/switch.c           |   5 +
> >  13 files changed, 727 insertions(+), 205 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
> >
>
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