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

From: Kalesh Singh
Date: Fri Jul 15 2022 - 20:04:27 EST

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In reply to: Kalesh Singh: "Re: [PATCH v4 00/18] KVM nVHE Hypervisor stack unwinder"
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On Fri, Jul 15, 2022 at 11:58 AM Kalesh Singh <kaleshsingh@xxxxxxxxxx> wrote:
>
> On Fri, Jul 15, 2022 at 6:55 AM 'Fuad Tabba' via kernel-team
> <kernel-team@xxxxxxxxxxx> wrote:
> >
> > Hi Kalesh,
> >
> > On Fri, Jul 15, 2022 at 7:10 AM Kalesh Singh <kaleshsingh@xxxxxxxxxx> 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@xxxxxxxxxx/
> > > v2: https://lore.kernel.org/r/20220502191222.4192768-1-kaleshsingh@xxxxxxxxxx/
> > > v1: https://lore.kernel.org/r/20220427184716.1949239-1-kaleshsingh@xxxxxxxxxx/
> > >
> > > 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.

My local config had CONFIG_RANDOMIZE_BASE off. I have posted a fix for
the existing occurrences [1]. I'll address those for the unwinder in
the next version of this series.

[1] https://lore.kernel.org/r/20220715235824.2549012-1-kaleshsingh@xxxxxxxxxx/

Thanks,
Kalesh

>
> --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
> > >
> >
> > --
> > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx.
> >

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In reply to: Kalesh Singh: "Re: [PATCH v4 00/18] KVM nVHE Hypervisor stack unwinder"
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