On Tue, Sep 22, 2009 at 09:59:04AM +0300, Avi Kivity wrote:
> On 09/22/2009 02:37 AM, Marcelo Tosatti wrote:
>> Use two steps for memslot deletion: mark the slot invalid (which stops
>> instantiation of new shadow pages for that slot, but allows destruction),
>> then instantiate the new empty slot.
>>
>> Also simplifies kvm_handle_hva locking.
>>
>> unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm)
>> {
>> - int i;
>> + int i, idx;
>> unsigned int nr_mmu_pages;
>> unsigned int nr_pages = 0;
>> + struct kvm_memslots *slots;
>>
>> - for (i = 0; i< kvm->memslots->nmemslots; i++)
>> - nr_pages += kvm->memslots->memslots[i].npages;
>> + idx = srcu_read_lock(&kvm->srcu);
>>
>
> Doesn't the caller hold the srcu_read_lock() here?
No:
kvm_vm_ioctl_set_nr_mmu_pages -> kvm_mmu_change_mmu_pages
And even if the caller did, recursive "locking" is tolerated.
>> Index: kvm-slotslock/arch/x86/kvm/vmx.c
>> ===================================================================
>> --- kvm-slotslock.orig/arch/x86/kvm/vmx.c
>> +++ kvm-slotslock/arch/x86/kvm/vmx.c
>> @@ -24,6 +24,7 @@
>> #include<linux/mm.h>
>> #include<linux/highmem.h>
>> #include<linux/sched.h>
>> +#include<linux/srcu.h>
>> #include<linux/moduleparam.h>
>> #include<linux/ftrace_event.h>
>> #include "kvm_cache_regs.h"
>> @@ -1465,10 +1466,18 @@ static void enter_pmode(struct kvm_vcpu
>> static gva_t rmode_tss_base(struct kvm *kvm)
>> {
>> if (!kvm->arch.tss_addr) {
>> - gfn_t base_gfn = kvm->memslots->memslots[0].base_gfn +
>> - kvm->memslots->memslots[0].npages - 3;
>> + struct kvm_memslots *slots;
>> + gfn_t base_gfn;
>> + int idx;
>> +
>> + idx = srcu_read_lock(&kvm->srcu);
>> + slots = rcu_dereference(kvm->memslots);
>> + base_gfn = slots->memslots[0].base_gfn +
>> + slots->memslots[0].npages - 3;
>> + srcu_read_unlock(&kvm->srcu, idx);
>> return base_gfn<< PAGE_SHIFT;
>> }
>> +
>>
>
> And here?
kvm_arch_vcpu_ioctl_set_sregs -> kvm_x86_ops->set_cr0.
> Maybe we should take the srcu_lock in vcpu_load/put and only
> drop in when going into vcpu context or explicitly sleeping, just to
> simplify things.
Hum, possible, but i'd rather leave it for later.
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