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

[Marc Zyngier <marc.zyngier@arm.com>]

On 26/08/14 12:43, Christoffer Dall 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@linaro.org>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

Acked-by: Marc Zyngier <marc.zyngier@arm.com>

	M.

> ---
> 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@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))
> 


-- 
Jazz is not dead. It just smells funny...