linux-kernel - [PATCH 0/2] Dump instructions on panic for pKVM/nvhe

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Message-ID: <20250717234744.2254371-1-smostafa@google.com>
Date: Thu, 17 Jul 2025 23:47:42 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	kvmarm@...ts.linux.dev
Cc: catalin.marinas@....com, will@...nel.org, maz@...nel.org, 
	oliver.upton@...ux.dev, joey.gouly@....com, suzuki.poulose@....com, 
	yuzenghui@...wei.com, qperret@...gle.com, keirf@...gle.com, 
	Mostafa Saleh <smostafa@...gle.com>
Subject: [PATCH 0/2] Dump instructions on panic for pKVM/nvhe

This small series, adds support for dumping the faulting instructions on
panic in pKVM and nvhe, similarly to what the kernel does as follow:
[   12.012126] kvm [190]: nVHE hyp BUG at: [<ffff8000811c5f64>] __kvm_nvhe_handle___kvm_vcpu_run+0x4/0x8!
[   12.015747] kvm [190]: Cannot dump pKVM nVHE stacktrace: !CONFIG_PROTECTED_NVHE_STACKTRACE
[   12.016044] Code: a8c17bfd d50323bf d65f03c0 d503245f (d4210000)
[   12.016082] kvm [190]: Hyp Offset: 0xffeff6887fe00000
[   12.016325] Kernel panic - not syncing: HYP panic:
[   12.016325] PS:204023c9 PC:000f8978013c5f64 ESR:00000000f2000800
[   12.016325] FAR:fff00000c016e01c HPFAR:00000000010016e0 PAR:0000000000000000

This can be useful in debugging cases of memory corruption.

The first patch adds this for nvhe and CONFIG_NVHE_EL2_DEBUG which is
straightforward as at the point of panic there is no stage-2 for the
host CPU, so it can re-use the kernel code to read and dump the faulting
instructions.

The second patch adds this support for pKVM, I splitted that into patches
as the pKVM changes are more fundamental, as now the hypervisor text would
be mapped in the host stage-2 as RO all the time.
An alternative is to make the hypervisor read its instructions on panic and
passes it to the kernel panic handler, but as we are out of registers
(X0-X7 used) for the arguments we would have to move that code to assembly.

Mostafa Saleh (2):
  KVM: arm64: Dump instruction on hyp panic
  KVM: arm64: Map hyp text as RO and dump instr on panic

 arch/arm64/include/asm/traps.h  |  1 +
 arch/arm64/kernel/traps.c       | 20 +++++++++++++-------
 arch/arm64/kvm/handle_exit.c    |  3 +++
 arch/arm64/kvm/hyp/nvhe/setup.c | 12 ++++++++++--
 4 files changed, 27 insertions(+), 9 deletions(-)

-- 
2.50.0.727.gbf7dc18ff4-goog