[PATCH v3 2/2] arm/arm64: KVM: Support KVM_CAP_READONLY_MEM

[Ard Biesheuvel]

On 26 August 2014 13:43, Christoffer Dall <christoffer.dall at linaro.org> wrote:
> When userspace loads code and data in a read-only memory regions, KVM
> needs to be able to handle this on arm and arm64.  Specifically this is
> used when running code directly from a read-only flash device; the
> common scenario is a UEFI blob loaded with the -bios option in QEMU.
>
> Note that the MMIO exit on writes to a read-only memory is ABI and can
> be used to emulate block-erase style flash devices.
>
> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>

Tested-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

Are these on track for 3.18?


> ---
> Changelog[v3]:
>  - Remove the check for fault_status != FSC_FAULT in the I/O memory
>    abort section, since we now do support permission faults on I/O
>    regions.  Reported-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Changelog[v2]:
>  - None
>
>  arch/arm/include/uapi/asm/kvm.h   |  1 +
>  arch/arm/kvm/arm.c                |  1 +
>  arch/arm/kvm/mmu.c                | 22 ++++++++--------------
>  arch/arm64/include/uapi/asm/kvm.h |  1 +
>  4 files changed, 11 insertions(+), 14 deletions(-)
>
> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
> index e6ebdd3..51257fd 100644
> --- a/arch/arm/include/uapi/asm/kvm.h
> +++ b/arch/arm/include/uapi/asm/kvm.h
> @@ -25,6 +25,7 @@
>
>  #define __KVM_HAVE_GUEST_DEBUG
>  #define __KVM_HAVE_IRQ_LINE
> +#define __KVM_HAVE_READONLY_MEM
>
>  #define KVM_REG_SIZE(id)                                               \
>         (1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 9f788eb..ac306b4 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -188,6 +188,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>         case KVM_CAP_ONE_REG:
>         case KVM_CAP_ARM_PSCI:
>         case KVM_CAP_ARM_PSCI_0_2:
> +       case KVM_CAP_READONLY_MEM:
>                 r = 1;
>                 break;
>         case KVM_CAP_COALESCED_MMIO:
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 16e7994..62f5642 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -747,14 +747,13 @@ static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
>  }
>
>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> -                         struct kvm_memory_slot *memslot,
> +                         struct kvm_memory_slot *memslot, unsigned long hva,
>                           unsigned long fault_status)
>  {
>         int ret;
>         bool write_fault, writable, hugetlb = false, force_pte = false;
>         unsigned long mmu_seq;
>         gfn_t gfn = fault_ipa >> PAGE_SHIFT;
> -       unsigned long hva = gfn_to_hva(vcpu->kvm, gfn);
>         struct kvm *kvm = vcpu->kvm;
>         struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
>         struct vm_area_struct *vma;
> @@ -863,7 +862,8 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>         unsigned long fault_status;
>         phys_addr_t fault_ipa;
>         struct kvm_memory_slot *memslot;
> -       bool is_iabt;
> +       unsigned long hva;
> +       bool is_iabt, write_fault, writable;
>         gfn_t gfn;
>         int ret, idx;
>
> @@ -884,7 +884,10 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>         idx = srcu_read_lock(&vcpu->kvm->srcu);
>
>         gfn = fault_ipa >> PAGE_SHIFT;
> -       if (!kvm_is_visible_gfn(vcpu->kvm, gfn)) {
> +       memslot = gfn_to_memslot(vcpu->kvm, gfn);
> +       hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
> +       write_fault = kvm_is_write_fault(kvm_vcpu_get_hsr(vcpu));
> +       if (kvm_is_error_hva(hva) || (write_fault && !writable)) {
>                 if (is_iabt) {
>                         /* Prefetch Abort on I/O address */
>                         kvm_inject_pabt(vcpu, kvm_vcpu_get_hfar(vcpu));
> @@ -892,13 +895,6 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>                         goto out_unlock;
>                 }
>
> -               if (fault_status != FSC_FAULT) {
> -                       kvm_err("Unsupported fault status on io memory: %#lx\n",
> -                               fault_status);
> -                       ret = -EFAULT;
> -                       goto out_unlock;
> -               }
> -
>                 /*
>                  * The IPA is reported as [MAX:12], so we need to
>                  * complement it with the bottom 12 bits from the
> @@ -910,9 +906,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>                 goto out_unlock;
>         }
>
> -       memslot = gfn_to_memslot(vcpu->kvm, gfn);
> -
> -       ret = user_mem_abort(vcpu, fault_ipa, memslot, fault_status);
> +       ret = user_mem_abort(vcpu, fault_ipa, memslot, hva, fault_status);
>         if (ret == 0)
>                 ret = 1;
>  out_unlock:
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index e633ff8..f4ec5a6 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -37,6 +37,7 @@
>
>  #define __KVM_HAVE_GUEST_DEBUG
>  #define __KVM_HAVE_IRQ_LINE
> +#define __KVM_HAVE_READONLY_MEM
>
>  #define KVM_REG_SIZE(id)                                               \
>         (1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))
> --
> 2.0.0
>