Re: KVM: MMU: add KVM_ZAP_GFN ioctl

Avi Kivity
2008-03-20T12:09:15Z

Marcelo Tosatti wrote:
> Add an ioctl to zap all mappings to a given gfn. This allows userspace
> remove the QEMU process mappings and the page without causing
> inconsistency.
>
>

I'm thinking of comitting rmap_nuke() to kvm.git, and the rest to the
external module, since this is only needed on kernels without mmu notifiers.

Andrea, is rmap_nuke() suitable for the mmu notifiers pte clear callback?

Oh, and a single gfn may have multiple hvas, so we need to iterate over
something here.

> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index f0cdfba..c41464f 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -642,6 +642,67 @@ static void rmap_write_protect(struct kvm *kvm, u64 gfn)
> account_shadowed(kvm, gfn);
> }
>
> +static void rmap_nuke(struct kvm *kvm, u64 gfn)
> +{
> + unsigned long *rmapp;
> + u64 *spte;
> + int nuked = 0;
> +
> + gfn = unalias_gfn(kvm, gfn);
> + rmapp = gfn_to_rmap(kvm, gfn, 0);
> +
> + spte = rmap_next(kvm, rmapp, NULL);
> + while (spte) {
> + BUG_ON(!spte);
> + BUG_ON(!(*spte & PT_PRESENT_MASK));
> + rmap_printk("rmap_nuke: spte %p %llx\n", spte, *spte);
> + rmap_remove(kvm, spte);
> + set_shadow_pte(spte, shadow_trap_nonpresent_pte);
> + nuked = 1;
> + spte = rmap_next(kvm, rmapp, spte);
> + }
> + /* check for huge page mappings */
> + rmapp = gfn_to_rmap(kvm, gfn, 1);
> + spte = rmap_next(kvm, rmapp, NULL);
> + while (spte) {
> + BUG_ON(!spte);
> + BUG_ON(!(*spte & PT_PRESENT_MASK));
> + BUG_ON((*spte & (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK)) != (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK));
> + pgprintk("rmap_nuke(large): spte %p %llx %lld\n", spte, *spte, gfn);
> + rmap_remove(kvm, spte);
> + --kvm->stat.lpages;
> + set_shadow_pte(spte, shadow_trap_nonpresent_pte);
> + nuked = 1;
> + spte = rmap_next(kvm, rmapp, spte);
> + }
> +
> + if (nuked)
> + kvm_flush_remote_tlbs(kvm);
> +}
> +
> +int kvm_zap_single_gfn(struct kvm *kvm, gfn_t gfn)
> +{
> + unsigned long addr;
> + int have_mmu_notifiers = 0;
> +
> + down_read(&kvm->slots_lock);
> + addr = gfn_to_hva(kvm, gfn);
> +
> + if (kvm_is_error_hva(addr)) {
> + up_read(&kvm->slots_lock);
> + return -EINVAL;
> + }
> +
> + if (!have_mmu_notifiers) {
> + spin_lock(&kvm->mmu_lock);
> + rmap_nuke(kvm, gfn);
> + spin_unlock(&kvm->mmu_lock);
> + }
> + up_read(&kvm->slots_lock);
> +
> + return 0;
> +}
> +
> #ifdef MMU_DEBUG
> static int is_empty_shadow_page(u64 *spt)
> {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e65a9d6..d982ca1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -816,6 +816,9 @@ int kvm_dev_ioctl_check_extension(long ext)
> case KVM_CAP_NR_MEMSLOTS:
> r = KVM_MEMORY_SLOTS;
> break;
> + case KVM_CAP_ZAP_GFN:
> + r = 1;
> + break;
> default:
> r = 0;
> break;
> @@ -1636,6 +1639,15 @@ long kvm_arch_vm_ioctl(struct file *filp,
> r = 0;
> break;
> }
> + case KVM_ZAP_GFN: {
> + gfn_t gfn;
> +
> + r = -EFAULT;
> + if (copy_from_user(&gfn, argp, sizeof gfn))
> + goto out;
> + r = kvm_zap_single_gfn(kvm, gfn);
> + break;
> + }
> default:
> ;
> }
> diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
> index 024b57c..4e45bd2 100644
> --- a/include/asm-x86/kvm_host.h
> +++ b/include/asm-x86/kvm_host.h
> @@ -425,6 +425,7 @@ void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte);
> int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
> void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
> void kvm_mmu_zap_all(struct kvm *kvm);
> +int kvm_zap_single_gfn(struct kvm *kvm, gfn_t gfn);
> unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
> void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
>
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index e92e703..9ea714f 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -236,6 +236,7 @@ struct kvm_vapic_addr {
> #define KVM_CAP_CLOCKSOURCE 8
> #define KVM_CAP_NR_VCPUS 9 /* returns max vcpus per vm */
> #define KVM_CAP_NR_MEMSLOTS 10 /* returns max memory slots per vm */
> +#define KVM_CAP_ZAP_GFN 11
>
> /*
> * ioctls for VM fds
> @@ -258,6 +259,7 @@ struct kvm_vapic_addr {
> #define KVM_IRQ_LINE _IOW(KVMIO, 0x61, struct kvm_irq_level)
> #define KVM_GET_IRQCHIP _IOWR(KVMIO, 0x62, struct kvm_irqchip)
> #define KVM_SET_IRQCHIP _IOR(KVMIO, 0x63, struct kvm_irqchip)
> +#define KVM_ZAP_GFN _IOR(KVMIO, 0x64, unsigned long)
>
> /*
> * ioctls for vcpu fds
>
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--
error compiling committee.c: too many arguments to function