linux-kernel - Re: [PATCH v4 07/18] KVM: arm64: On stack overflow switch to hyp overflow

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Message-ID: <CA+EHjTxrdacNE-kd2kUSHRZXdgtLZkzwZcamiHaAW4=yfGWtwQ@mail.gmail.com>
Date:   Mon, 18 Jul 2022 10:46:06 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     maz@...nel.org, mark.rutland@....com, broonie@...nel.org,
        madvenka@...ux.microsoft.com, will@...nel.org, qperret@...gle.com,
        james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com,
        andreyknvl@...il.com, russell.king@...cle.com,
        vincenzo.frascino@....com, mhiramat@...nel.org, ast@...nel.org,
        drjones@...hat.com, wangkefeng.wang@...wei.com, elver@...gle.com,
        keirf@...gle.com, yuzenghui@...wei.com, ardb@...nel.org,
        oupton@...gle.com, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        android-mm@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH v4 07/18] KVM: arm64: On stack overflow switch to hyp overflow_stack

Hi Kalesh,

On Fri, Jul 15, 2022 at 7:11 AM Kalesh Singh <kaleshsingh@...gle.com> wrote:
>
> On hyp stack overflow switch to 16-byte aligned secondary stack.
> This provides us stack space to better handle overflows; and is
> used in a subsequent patch to dump the hypervisor stacktrace.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>

Reviewed-by: Fuad Tabba <tabba@...gle.com>

Thanks,
/fuad


> ---
>  arch/arm64/kvm/hyp/nvhe/Makefile     |  2 +-
>  arch/arm64/kvm/hyp/nvhe/host.S       |  9 ++-------
>  arch/arm64/kvm/hyp/nvhe/stacktrace.c | 11 +++++++++++
>  3 files changed, 14 insertions(+), 8 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/stacktrace.c
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index f9fe4dc21b1f..524e7dad5739 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -14,7 +14,7 @@ lib-objs := $(addprefix ../../../lib/, $(lib-objs))
>
>  obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
>          hyp-main.o hyp-smp.o psci-relay.o early_alloc.o page_alloc.o \
> -        cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o
> +        cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o stacktrace.o
>  obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
>          ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
>  obj-$(CONFIG_DEBUG_LIST) += list_debug.o
> diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
> index ea6a397b64a6..b6c0188c4b35 100644
> --- a/arch/arm64/kvm/hyp/nvhe/host.S
> +++ b/arch/arm64/kvm/hyp/nvhe/host.S
> @@ -177,13 +177,8 @@ SYM_FUNC_END(__host_hvc)
>         b       hyp_panic
>
>  .L__hyp_sp_overflow\@:
> -       /*
> -        * Reset SP to the top of the stack, to allow handling the hyp_panic.
> -        * This corrupts the stack but is ok, since we won't be attempting
> -        * any unwinding here.
> -        */
> -       ldr_this_cpu    x0, kvm_init_params + NVHE_INIT_STACK_HYP_VA, x1
> -       mov     sp, x0
> +       /* Switch to the overflow stack */
> +       adr_this_cpu sp, overflow_stack + OVERFLOW_STACK_SIZE, x0
>
>         b       hyp_panic_bad_stack
>         ASM_BUG()
> diff --git a/arch/arm64/kvm/hyp/nvhe/stacktrace.c b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> new file mode 100644
> index 000000000000..a3d5b34e1249
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> @@ -0,0 +1,11 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * KVM nVHE hypervisor stack tracing support.
> + *
> + * Copyright (C) 2022 Google LLC
> + */
> +#include <asm/memory.h>
> +#include <asm/percpu.h>
> +
> +DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
> +       __aligned(16);
> --
> 2.37.0.170.g444d1eabd0-goog
>