Commit 87727ba2 authored by Will Deacon's avatar Will Deacon
Browse files

KVM: arm64: Ensure CPU PMU probes before pKVM host de-privilege 



Although pKVM supports CPU PMU emulation for non-protected guests since
722625c6 ("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 7755cec6 ("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@linux.dev>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Fixes: 7755cec6 ("arm64: perf: Move PMUv3 driver to drivers/perf")
Tested-by: default avatarFuad Tabba <tabba@google.com>
Acked-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230420123356.2708-1-will@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 257aedb7

arch/arm64/kvm/arm.c

+0 −45
Original line number Diff line number Diff line
@@ -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) {

arch/arm64/kvm/pkvm.c

+47 −0
Original line number Diff line number Diff line
@@ -4,6 +4,8 @@ 
 * Author: Quentin Perret <qperret@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);