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x86/kvm: Disable preemption in kvm_flush_tlb_multi()

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kvm_flush_tlb_multi() is installed as an x86 PV TLB flush backend, so
flush_tlb_multi() can reach it through pv_ops when running as a KVM
guest.

kvm_flush_tlb_multi() uses the per-CPU scratch cpumask __pv_cpu_mask.
That buffer must remain tied to the current CPU until the mask has been
copied, filtered, and consumed by native_flush_tlb_multi().

The x86/mm callers currently enter flush_tlb_multi() while pinned to a
CPU. To let those callers drop CPU pinning before issuing the remote TLB
flush, each PV backend must protect its own CPU-local scratch state.

Make the KVM backend protect its per-CPU scratch cpumask by disabling
preemption locally. This is harmless with the current callers, where the
preemption disable is nested, and makes the KVM pv_ops dependency
explicit before changing the x86/mm call sites.

Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20260709122933.4021501-14-zhouchuyi@bytedance.com
This commit is contained in:
Chuyi Zhou 2026-07-09 20:29:32 +08:00 committed by Thomas Gleixner
parent ed15468787
commit ae397bb32d
1 changed files with 3 additions and 1 deletions
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4
arch/x86/kernel/kvm.c
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@ -663,8 +663,10 @@ static void kvm_flush_tlb_multi(const struct cpumask *cpumask,
u8 state;
int cpu;
struct kvm_steal_time *src;
struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask);
struct cpumask *flushmask;
guard(preempt)();
flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask);
cpumask_copy(flushmask, cpumask);
/*
* We have to call flush only on online vCPUs. And