linux-kernel - [PATCH v3 8/8] KVM: arm64: Symbolize the nVHE HYP backtrace

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Date:   Wed, 23 Feb 2022 21:13:43 -0800
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     will@...nel.org, maz@...nel.org, qperret@...gle.com,
        tabba@...gle.com, surenb@...gle.com, kernel-team@...roid.com,
        Kalesh Singh <kaleshsingh@...gle.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
        Andrew Walbran <qwandor@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 8/8] KVM: arm64: Symbolize the nVHE HYP backtrace

Reintroduce the __kvm_nvhe_ symbols in kallsyms, ignoring the local
symbols in this namespace. The local symbols are not informative and
can cause aliasing issues when symbolizing the addresses.

With the necessary symbols now in kallsyms we can symbolize nVHE
stacktrace addresses using the %pB print format specifier.

Example call trace:

[   98.916444][  T426] kvm [426]: nVHE hyp panic at: [<ffffffc0096156fc>] __kvm_nvhe_overflow_stack+0x8/0x34!
[   98.918360][  T426] nVHE HYP call trace:
[   98.918692][  T426] kvm [426]: [<ffffffc009615aac>] __kvm_nvhe_cpu_prepare_nvhe_panic_info+0x4c/0x68
[   98.919545][  T426] kvm [426]: [<ffffffc0096159a4>] __kvm_nvhe_hyp_panic+0x2c/0xe8
[   98.920107][  T426] kvm [426]: [<ffffffc009615ad8>] __kvm_nvhe_hyp_panic_bad_stack+0x10/0x10
[   98.920665][  T426] kvm [426]: [<ffffffc009610a4c>] __kvm_nvhe___kvm_hyp_host_vector+0x24c/0x794
[   98.921292][  T426] kvm [426]: [<ffffffc009615718>] __kvm_nvhe_overflow_stack+0x24/0x34
. . .

[   98.973382][  T426] kvm [426]: [<ffffffc009615718>] __kvm_nvhe_overflow_stack+0x24/0x34
[   98.973816][  T426] kvm [426]: [<ffffffc0096152f4>] __kvm_nvhe___kvm_vcpu_run+0x38/0x438
[   98.974255][  T426] kvm [426]: [<ffffffc009616f80>] __kvm_nvhe_handle___kvm_vcpu_run+0x1c4/0x364
[   98.974719][  T426] kvm [426]: [<ffffffc009616928>] __kvm_nvhe_handle_trap+0xa8/0x130
[   98.975152][  T426] kvm [426]: [<ffffffc009610064>] __kvm_nvhe___host_exit+0x64/0x64
[   98.975588][  T426] ---- end of nVHE HYP call trace ----

Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
---

Changes in v2:
  - Fix printk warnings - %p expects (void *)

 arch/arm64/kvm/handle_exit.c | 13 +++++--------
 scripts/kallsyms.c           |  2 +-
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index ff69dff33700..3a5c32017c6b 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -296,13 +296,8 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
 	u64 elr_in_kimg = __phys_to_kimg(elr_phys);
 	u64 hyp_offset = elr_in_kimg - kaslr_offset() - elr_virt;
 	u64 mode = spsr & PSR_MODE_MASK;
+	u64 panic_addr = elr_virt + hyp_offset;
 
-	/*
-	 * The nVHE hyp symbols are not included by kallsyms to avoid issues
-	 * with aliasing. That means that the symbols cannot be printed with the
-	 * "%pS" format specifier, so fall back to the vmlinux address if
-	 * there's no better option.
-	 */
 	if (mode != PSR_MODE_EL2t && mode != PSR_MODE_EL2h) {
 		kvm_err("Invalid host exception to nVHE hyp!\n");
 	} else if (ESR_ELx_EC(esr) == ESR_ELx_EC_BRK64 &&
@@ -322,9 +317,11 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
 		if (file)
 			kvm_err("nVHE hyp BUG at: %s:%u!\n", file, line);
 		else
-			kvm_err("nVHE hyp BUG at: %016llx!\n", elr_virt + hyp_offset);
+			kvm_err("nVHE hyp BUG at: [<%016llx>] %pB!\n", panic_addr,
+					(void *)panic_addr);
 	} else {
-		kvm_err("nVHE hyp panic at: %016llx!\n", elr_virt + hyp_offset);
+		kvm_err("nVHE hyp panic at: [<%016llx>] %pB!\n", panic_addr,
+				(void *)panic_addr);
 	}
 
 	kvm_nvhe_dump_backtrace(hyp_offset);
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 54ad86d13784..19aba43d9da4 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -111,7 +111,7 @@ static bool is_ignored_symbol(const char *name, char type)
 		".LASANPC",		/* s390 kasan local symbols */
 		"__crc_",		/* modversions */
 		"__efistub_",		/* arm64 EFI stub namespace */
-		"__kvm_nvhe_",		/* arm64 non-VHE KVM namespace */
+		"__kvm_nvhe_$",		/* arm64 local symbols in non-VHE KVM namespace */
 		"__AArch64ADRPThunk_",	/* arm64 lld */
 		"__ARMV5PILongThunk_",	/* arm lld */
 		"__ARMV7PILongThunk_",
-- 
2.35.1.473.g83b2b277ed-goog