[PATCH] KVM: arm64: Ensure CPU PMU probes before pKVM host de-privilege
Will Deacon
will at kernel.org
Thu Apr 20 05:33:56 PDT 2023
Although pKVM supports CPU PMU emulation for non-protected guests since
722625c6f4c5 ("KVM: arm64: Reenable pmu in Protected Mode"), this relies
on the PMU driver probing before the host has de-privileged so that the
'kvm_arm_pmu_available' static key can still be enabled by patching the
hypervisor text.
As it happens, both of these events hang off device_initcall() but the
PMU consistently won the race until 7755cec63ade ("arm64: perf: Move
PMUv3 driver to drivers/perf"). Since then, the host will fail to boot
when pKVM is enabled:
| hw perfevents: enabled with armv8_pmuv3_0 PMU driver, 7 counters available
| kvm [1]: nVHE hyp BUG at: [<ffff8000090366e0>] __kvm_nvhe_handle_host_mem_abort+0x270/0x284!
| kvm [1]: Cannot dump pKVM nVHE stacktrace: !CONFIG_PROTECTED_NVHE_STACKTRACE
| kvm [1]: Hyp Offset: 0xfffea41fbdf70000
| Kernel panic - not syncing: HYP panic:
| PS:a00003c9 PC:0000dbe04b0c66e0 ESR:00000000f2000800
| FAR:fffffbfffddfcf00 HPFAR:00000000010b0bf0 PAR:0000000000000000
| VCPU:0000000000000000
| CPU: 2 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc7-00083-g0bce6746d154 #1
| Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
| Call trace:
| dump_backtrace+0xec/0x108
| show_stack+0x18/0x2c
| dump_stack_lvl+0x50/0x68
| dump_stack+0x18/0x24
| panic+0x13c/0x33c
| nvhe_hyp_panic_handler+0x10c/0x190
| aarch64_insn_patch_text_nosync+0x64/0xc8
| arch_jump_label_transform+0x4c/0x5c
| __jump_label_update+0x84/0xfc
| jump_label_update+0x100/0x134
| static_key_enable_cpuslocked+0x68/0xac
| static_key_enable+0x20/0x34
| kvm_host_pmu_init+0x88/0xa4
| armpmu_register+0xf0/0xf4
| arm_pmu_acpi_probe+0x2ec/0x368
| armv8_pmu_driver_init+0x38/0x44
| do_one_initcall+0xcc/0x240
Fix the race properly by deferring the de-privilege step to
device_initcall_sync(). This will also be needed in future when probing
IOMMU devices and allows us to separate the pKVM de-privilege logic from
the core hypervisor initialisation path.
Cc: Oliver Upton <oliver.upton at linux.dev>
Cc: Fuad Tabba <tabba at google.com>
Cc: Marc Zyngier <maz at kernel.org>
Fixes: 7755cec63ade ("arm64: perf: Move PMUv3 driver to drivers/perf")
Signed-off-by: Will Deacon <will at kernel.org>
---
Marc, Oliver -- in practice, this issue only crops with the patches
moving the CPU PMU driver out into drivers/perf/ and so the arm64
for-next/core branch is broken. Please can I queue this in the arm64
tree for 6.4 with your Ack? Thanks.
arch/arm64/kvm/arm.c | 45 -----------------------------------------
arch/arm64/kvm/pkvm.c | 47 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 47 insertions(+), 45 deletions(-)
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 3bd732eaf087..890f730bc3ab 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -16,7 +16,6 @@
#include <linux/fs.h>
#include <linux/mman.h>
#include <linux/sched.h>
-#include <linux/kmemleak.h>
#include <linux/kvm.h>
#include <linux/kvm_irqfd.h>
#include <linux/irqbypass.h>
@@ -46,7 +45,6 @@
#include <kvm/arm_psci.h>
static enum kvm_mode kvm_mode = KVM_MODE_DEFAULT;
-DEFINE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
@@ -2105,41 +2103,6 @@ static int __init init_hyp_mode(void)
return err;
}
-static void __init _kvm_host_prot_finalize(void *arg)
-{
- int *err = arg;
-
- if (WARN_ON(kvm_call_hyp_nvhe(__pkvm_prot_finalize)))
- WRITE_ONCE(*err, -EINVAL);
-}
-
-static int __init pkvm_drop_host_privileges(void)
-{
- int ret = 0;
-
- /*
- * Flip the static key upfront as that may no longer be possible
- * once the host stage 2 is installed.
- */
- static_branch_enable(&kvm_protected_mode_initialized);
- on_each_cpu(_kvm_host_prot_finalize, &ret, 1);
- return ret;
-}
-
-static int __init finalize_hyp_mode(void)
-{
- if (!is_protected_kvm_enabled())
- return 0;
-
- /*
- * Exclude HYP sections from kmemleak so that they don't get peeked
- * at, which would end badly once inaccessible.
- */
- kmemleak_free_part(__hyp_bss_start, __hyp_bss_end - __hyp_bss_start);
- kmemleak_free_part_phys(hyp_mem_base, hyp_mem_size);
- return pkvm_drop_host_privileges();
-}
-
struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr)
{
struct kvm_vcpu *vcpu;
@@ -2257,14 +2220,6 @@ static __init int kvm_arm_init(void)
if (err)
goto out_hyp;
- if (!in_hyp_mode) {
- err = finalize_hyp_mode();
- if (err) {
- kvm_err("Failed to finalize Hyp protection\n");
- goto out_subs;
- }
- }
-
if (is_protected_kvm_enabled()) {
kvm_info("Protected nVHE mode initialized successfully\n");
} else if (in_hyp_mode) {
diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index cf56958b1492..6e9ece1ebbe7 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -4,6 +4,8 @@
* Author: Quentin Perret <qperret at google.com>
*/
+#include <linux/init.h>
+#include <linux/kmemleak.h>
#include <linux/kvm_host.h>
#include <linux/memblock.h>
#include <linux/mutex.h>
@@ -13,6 +15,8 @@
#include "hyp_constants.h"
+DEFINE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
+
static struct memblock_region *hyp_memory = kvm_nvhe_sym(hyp_memory);
static unsigned int *hyp_memblock_nr_ptr = &kvm_nvhe_sym(hyp_memblock_nr);
@@ -213,3 +217,46 @@ int pkvm_init_host_vm(struct kvm *host_kvm)
mutex_init(&host_kvm->lock);
return 0;
}
+
+static void __init _kvm_host_prot_finalize(void *arg)
+{
+ int *err = arg;
+
+ if (WARN_ON(kvm_call_hyp_nvhe(__pkvm_prot_finalize)))
+ WRITE_ONCE(*err, -EINVAL);
+}
+
+static int __init pkvm_drop_host_privileges(void)
+{
+ int ret = 0;
+
+ /*
+ * Flip the static key upfront as that may no longer be possible
+ * once the host stage 2 is installed.
+ */
+ static_branch_enable(&kvm_protected_mode_initialized);
+ on_each_cpu(_kvm_host_prot_finalize, &ret, 1);
+ return ret;
+}
+
+static int __init finalize_pkvm(void)
+{
+ int ret;
+
+ if (!is_protected_kvm_enabled())
+ return 0;
+
+ /*
+ * Exclude HYP sections from kmemleak so that they don't get peeked
+ * at, which would end badly once inaccessible.
+ */
+ kmemleak_free_part(__hyp_bss_start, __hyp_bss_end - __hyp_bss_start);
+ kmemleak_free_part_phys(hyp_mem_base, hyp_mem_size);
+
+ ret = pkvm_drop_host_privileges();
+ if (ret)
+ pr_err("Failed to finalize Hyp protection: %d\n", ret);
+
+ return ret;
+}
+device_initcall_sync(finalize_pkvm);
--
2.40.0.634.g4ca3ef3211-goog
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