Re: [RFC/RFT PATCH v2 2/3] KVM: promote KVM_MEMSLOT_INCOHERENT to uapi

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/05/2015 13:31, Andrew Jones wrote:
> Commit 1050dcda30529 introduced KVM_MEMSLOT_INCOHERENT to flag memory
> regions that may have coherency issues due to mapping host system RAM
> as non-cacheable. This was introduced as a KVM internal flag, but now
> give KVM userspace access to it so that it may use it for hinting
> likely problematic regions. Also rename to KVM_MEM_UNCACHED.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  Documentation/virtual/kvm/api.txt | 20 ++++++++++++++------
>  arch/arm/include/uapi/asm/kvm.h   |  1 +
>  arch/arm/kvm/arm.c                |  1 +
>  arch/arm/kvm/mmu.c                |  4 ++--
>  arch/arm64/include/uapi/asm/kvm.h |  1 +
>  include/linux/kvm_host.h          |  1 -
>  include/uapi/linux/kvm.h          |  2 ++
>  virt/kvm/kvm_main.c               |  7 ++++++-
>  8 files changed, 27 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 9fa2bf8c3f6f1..04ffd9f5db5f2 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -905,6 +905,7 @@ struct kvm_userspace_memory_region {
>  /* for kvm_memory_region::flags */
>  #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
>  #define KVM_MEM_READONLY	(1UL << 1)
> +#define KVM_MEM_UNCACHED	(1UL << 2)
>  
>  This ioctl allows the user to create or modify a guest physical memory
>  slot.  When changing an existing slot, it may be moved in the guest
> @@ -920,12 +921,19 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
>  be identical.  This allows large pages in the guest to be backed by large
>  pages in the host.
>  
> -The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
> -KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
> -writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
> -use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
> -to make a new slot read-only.  In this case, writes to this memory will be
> -posted to userspace as KVM_EXIT_MMIO exits.
> +The flags field supports the following flags. All flags may be used in
> +combination.
> +  - KVM_MEM_LOG_DIRTY_PAGES: no capability required
> +      Set this to instruct KVM to keep track of writes to memory within
> +      the slot. (See the KVM_GET_DIRTY_LOG ioctl)
> +  - KVM_MEM_READONLY: depends on capability KVM_CAP_READONLY_MEM
> +      Set this to make a new slot read-only. In this case, writes to
> +      this memory will be posted to userspace as KVM_EXIT_MMIO exits.
> +      EINVAL will be returned if the slot is not new.
> +  - KVM_MEM_UNCACHED: depends on capability KVM_CAP_UNCACHED_MEM
> +      Set this to make a new slot uncached, i.e. userspace will always
> +      directly read/write RAM for this memory region. EINVAL will be
> +      returned if the slot is not new.
>  
>  When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of
>  the memory region are automatically reflected into the guest.  For example, an
> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
> index df3f60cb1168a..893a331655115 100644
> --- a/arch/arm/include/uapi/asm/kvm.h
> +++ b/arch/arm/include/uapi/asm/kvm.h
> @@ -26,6 +26,7 @@
>  #define __KVM_HAVE_GUEST_DEBUG
>  #define __KVM_HAVE_IRQ_LINE
>  #define __KVM_HAVE_READONLY_MEM
> +#define __KVM_HAVE_UNCACHED_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 d9631ecddd56e..cbb532de9c8b5 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -182,6 +182,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_ARM_PSCI_0_2:
>  	case KVM_CAP_READONLY_MEM:
>  	case KVM_CAP_MP_STATE:
> +	case KVM_CAP_UNCACHED_MEM:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 1d5accbd3dcf2..bc1665acd73e7 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -1307,7 +1307,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	if (!hugetlb && !force_pte)
>  		hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
>  
> -	fault_ipa_uncached = memslot->flags & KVM_MEMSLOT_INCOHERENT;
> +	fault_ipa_uncached = memslot->flags & KVM_MEM_UNCACHED;
>  
>  	if (hugetlb) {
>  		pmd_t new_pmd = pfn_pmd(pfn, mem_type);
> @@ -1834,7 +1834,7 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
>  	 * regions as incoherent.
>  	 */
>  	if (slot->flags & KVM_MEM_READONLY)
> -		slot->flags |= KVM_MEMSLOT_INCOHERENT;
> +		slot->flags |= KVM_MEM_UNCACHED;
>  	return 0;
>  }
>  
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index d26832022127e..be46855ca01b7 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -38,6 +38,7 @@
>  #define __KVM_HAVE_GUEST_DEBUG
>  #define __KVM_HAVE_IRQ_LINE
>  #define __KVM_HAVE_READONLY_MEM
> +#define __KVM_HAVE_UNCACHED_MEM
>  
>  #define KVM_REG_SIZE(id)						\
>  	(1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index ad45054309a0f..74d6a14529f53 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -39,7 +39,6 @@
>   * include/linux/kvm_h.
>   */
>  #define KVM_MEMSLOT_INVALID	(1UL << 16)
> -#define KVM_MEMSLOT_INCOHERENT	(1UL << 17)
>  
>  /* Two fragments for cross MMIO pages. */
>  #define KVM_MAX_MMIO_FRAGMENTS	2
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4b60056776d14..ceb6e805e5f77 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -108,6 +108,7 @@ struct kvm_userspace_memory_region {
>   */
>  #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
>  #define KVM_MEM_READONLY	(1UL << 1)
> +#define KVM_MEM_UNCACHED	(1UL << 2)
>  
>  /* for KVM_IRQ_LINE */
>  struct kvm_irq_level {
> @@ -814,6 +815,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_S390_INJECT_IRQ 113
>  #define KVM_CAP_S390_IRQ_STATE 114
>  #define KVM_CAP_PPC_HWRNG 115
> +#define KVM_CAP_UNCACHED_MEM 116
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 90977418aeb6e..d1d535d80a075 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -719,6 +719,10 @@ static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
>  	valid_flags |= KVM_MEM_READONLY;
>  #endif
>  
> +#ifdef __KVM_HAVE_UNCACHED_MEM
> +	valid_flags |= KVM_MEM_UNCACHED;
> +#endif
> +
>  	if (mem->flags & ~valid_flags)
>  		return -EINVAL;
>  
> @@ -816,7 +820,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  		else { /* Modify an existing slot. */
>  			if ((mem->userspace_addr != old.userspace_addr) ||
>  			    (npages != old.npages) ||
> -			    ((new.flags ^ old.flags) & KVM_MEM_READONLY))
> +			    ((new.flags ^ old.flags) &
> +			     (KVM_MEM_READONLY | KVM_MEM_UNCACHED)))
>  				goto out;
>  
>  			if (base_gfn != old.base_gfn)
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>