Re: [PATCH v2] KVM: Check the allocation of pv cpu mask

[Haiwei Li]

On 20/9/3 18:39, Vitaly Kuznetsov wrote:
Haiwei Li <lihaiwei.ker...@gmail.com> writes:

From: Haiwei Li <lihai...@tencent.com>

check the allocation of per-cpu __pv_cpu_mask. Initialize ops only when
successful.

Signed-off-by: Haiwei Li <lihai...@tencent.com>
---
   arch/x86/kernel/kvm.c | 24 ++++++++++++++++++++----
   1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 08320b0b2b27..d3c062e551d7 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -555,7 +555,6 @@ static void kvm_send_ipi_mask_allbutself(const
struct cpumask *mask, int vector)
   static void kvm_setup_pv_ipi(void)
   {
        apic->send_IPI_mask = kvm_send_ipi_mask;
-       apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself;
        pr_info("setup PV IPIs\n");
   }

@@ -654,7 +653,6 @@ static void __init kvm_guest_init(void)
        }

        if (pv_tlb_flush_supported()) {
-               pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others;
                pv_ops.mmu.tlb_remove_table = tlb_remove_table;
                pr_info("KVM setup pv remote TLB flush\n");
        }
@@ -767,6 +765,14 @@ static __init int activate_jump_labels(void)
   }
   arch_initcall(activate_jump_labels);

+static void kvm_free_pv_cpu_mask(void)
+{
+       unsigned int cpu;
+
+       for_each_possible_cpu(cpu)
+               free_cpumask_var(per_cpu(__pv_cpu_mask, cpu));
+}
+
   static __init int kvm_alloc_cpumask(void)
   {
        int cpu;
@@ -785,11 +791,21 @@ static __init int kvm_alloc_cpumask(void)

        if (alloc)
                for_each_possible_cpu(cpu) {
-                       zalloc_cpumask_var_node(per_cpu_ptr(&__pv_cpu_mask, 
cpu),
-                               GFP_KERNEL, cpu_to_node(cpu));
+                       if (!zalloc_cpumask_var_node(
+                               per_cpu_ptr(&__pv_cpu_mask, cpu),
+                               GFP_KERNEL, cpu_to_node(cpu)))
+                               goto zalloc_cpumask_fail;
                }

+#if defined(CONFIG_SMP)
+       apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself;
+#endif
+       pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others;

This is too late I'm afraid. If I'm not mistaken PV patching happens
earlier, so .init.guest_late_init (kvm_guest_init()) is good and
arch_initcall() is bad.

.init.guest_late_init (kvm_guest_init()) is called before 
arch_initcall() and kvm_flush_tlb_others && kvm_send_ipi_mask_allbutself 
rely on __pv_cpu_mask.  So, i can not put this assign in kvm_guest_init().


Have you checked that with this patch kvm_flush_tlb_others() is still
being called?

yes. I add a printk and i get the log.


Actually, there is no need to assign kvm_flush_tlb_others() so late. We
can always check if __pv_cpu_mask was allocated and revert back to the
architectural path if not.
I am sorry i don't really understand. Can you explain in more detail? Thx.


        return 0;
+
+zalloc_cpumask_fail:
+       kvm_free_pv_cpu_mask();
+       return -ENOMEM;
   }
   arch_initcall(kvm_alloc_cpumask);

--
2.18.4