6.6-stable review patch. If anyone has any objections, please let me know.
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From: Mark Rutland mark.rutland@arm.com
[ Upstream commit 20f3b8eafe0ba5d3c69d5011a9b07739e9645132 ]
When KPTI is in use, we cannot register a runstate region as XEN requires that this is always a valid VA, which we cannot guarantee. Due to this, xen_starting_cpu() must avoid registering each CPU's runstate region, and xen_guest_init() must avoid setting up features that depend upon it.
We tried to ensure that in commit:
f88af7229f6f22ce (" xen/arm: do not setup the runstate info page if kpti is enabled")
... where we added checks for xen_kernel_unmapped_at_usr(), which wraps arm64_kernel_unmapped_at_el0() on arm64 and is always false on 32-bit arm.
Unfortunately, as xen_guest_init() is an early_initcall, this happens before secondary CPUs are booted and arm64 has finalized the ARM64_UNMAP_KERNEL_AT_EL0 cpucap which backs arm64_kernel_unmapped_at_el0(), and so this can subsequently be set as secondary CPUs are onlined. On a big.LITTLE system where the boot CPU does not require KPTI but some secondary CPUs do, this will result in xen_guest_init() intializing features that depend on the runstate region, and xen_starting_cpu() registering the runstate region on some CPUs before KPTI is subsequent enabled, resulting the the problems the aforementioned commit tried to avoid.
Handle this more robsutly by deferring the initialization of the runstate region until secondary CPUs have been initialized and the ARM64_UNMAP_KERNEL_AT_EL0 cpucap has been finalized. The per-cpu work is moved into a new hotplug starting function which is registered later when we're certain that KPTI will not be used.
Fixes: f88af7229f6f ("xen/arm: do not setup the runstate info page if kpti is enabled") Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Bertrand Marquis bertrand.marquis@arm.com Cc: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: Juergen Gross jgross@suse.com Cc: Stefano Stabellini sstabellini@kernel.org Cc: Suzuki K Poulose suzuki.poulose@arm.com Cc: Will Deacon will@kernel.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm/xen/enlighten.c | 25 ++++++++++++++++--------- include/linux/cpuhotplug.h | 1 + 2 files changed, 17 insertions(+), 9 deletions(-)
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c index c392e18f1e431..9afdc4c4a5dc1 100644 --- a/arch/arm/xen/enlighten.c +++ b/arch/arm/xen/enlighten.c @@ -164,9 +164,6 @@ static int xen_starting_cpu(unsigned int cpu) BUG_ON(err); per_cpu(xen_vcpu, cpu) = vcpup;
- if (!xen_kernel_unmapped_at_usr()) - xen_setup_runstate_info(cpu); - after_register_vcpu_info: enable_percpu_irq(xen_events_irq, 0); return 0; @@ -523,9 +520,6 @@ static int __init xen_guest_init(void) return -EINVAL; }
- if (!xen_kernel_unmapped_at_usr()) - xen_time_setup_guest(); - if (xen_initial_domain()) pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
@@ -535,7 +529,13 @@ static int __init xen_guest_init(void) } early_initcall(xen_guest_init);
-static int __init xen_pm_init(void) +static int xen_starting_runstate_cpu(unsigned int cpu) +{ + xen_setup_runstate_info(cpu); + return 0; +} + +static int __init xen_late_init(void) { if (!xen_domain()) return -ENODEV; @@ -548,9 +548,16 @@ static int __init xen_pm_init(void) do_settimeofday64(&ts); }
- return 0; + if (xen_kernel_unmapped_at_usr()) + return 0; + + xen_time_setup_guest(); + + return cpuhp_setup_state(CPUHP_AP_ARM_XEN_RUNSTATE_STARTING, + "arm/xen_runstate:starting", + xen_starting_runstate_cpu, NULL); } -late_initcall(xen_pm_init); +late_initcall(xen_late_init);
/* empty stubs */ diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h index 068f7738be22a..28c1d3d77b70f 100644 --- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h @@ -189,6 +189,7 @@ enum cpuhp_state { /* Must be the last timer callback */ CPUHP_AP_DUMMY_TIMER_STARTING, CPUHP_AP_ARM_XEN_STARTING, + CPUHP_AP_ARM_XEN_RUNSTATE_STARTING, CPUHP_AP_ARM_CORESIGHT_STARTING, CPUHP_AP_ARM_CORESIGHT_CTI_STARTING, CPUHP_AP_ARM64_ISNDEP_STARTING,