Re: [PATCH v5 12/13] KVM: Expose KVM_MEM_PRIVATE
From: Sean Christopherson <seanjc@google.com>
Date: 2022-03-29 19:13:09
Also in:
kvm, linux-fsdevel, linux-mm, lkml, qemu-devel
On Thu, Mar 10, 2022, Chao Peng wrote:
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KVM_MEM_PRIVATE is not exposed by default but architecture code can turn on it by implementing kvm_arch_private_memory_supported(). Signed-off-by: Yu Zhang <redacted> Signed-off-by: Chao Peng <redacted> --- include/linux/kvm_host.h | 1 + virt/kvm/kvm_main.c | 24 +++++++++++++++++++----- 2 files changed, 20 insertions(+), 5 deletions(-)diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 186b9b981a65..0150e952a131 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h@@ -1432,6 +1432,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu); int kvm_arch_post_init_vm(struct kvm *kvm); void kvm_arch_pre_destroy_vm(struct kvm *kvm); int kvm_arch_create_vm_debugfs(struct kvm *kvm); +bool kvm_arch_private_memory_supported(struct kvm *kvm); #ifndef __KVM_HAVE_ARCH_VM_ALLOC /*diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 52319f49d58a..df5311755a40 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c@@ -1485,10 +1485,19 @@ static void kvm_replace_memslot(struct kvm *kvm, } } -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem) +bool __weak kvm_arch_private_memory_supported(struct kvm *kvm) +{ + return false; +} + +static int check_memory_region_flags(struct kvm *kvm, + const struct kvm_userspace_memory_region *mem) { u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES; + if (kvm_arch_private_memory_supported(kvm)) + valid_flags |= KVM_MEM_PRIVATE; + #ifdef __KVM_HAVE_READONLY_MEM valid_flags |= KVM_MEM_READONLY; #endif@@ -1900,7 +1909,7 @@ int __kvm_set_memory_region(struct kvm *kvm, int as_id, id; int r; - r = check_memory_region_flags(mem); + r = check_memory_region_flags(kvm, mem); if (r) return r;@@ -1913,10 +1922,12 @@ int __kvm_set_memory_region(struct kvm *kvm, return -EINVAL; if (mem->guest_phys_addr & (PAGE_SIZE - 1)) return -EINVAL; - /* We can read the guest memory with __xxx_user() later on. */ if ((mem->userspace_addr & (PAGE_SIZE - 1)) || - (mem->userspace_addr != untagged_addr(mem->userspace_addr)) || - !access_ok((void __user *)(unsigned long)mem->userspace_addr, + (mem->userspace_addr != untagged_addr(mem->userspace_addr))) + return -EINVAL; + /* We can read the guest memory with __xxx_user() later on. */ + if (!(mem->flags & KVM_MEM_PRIVATE) && + !access_ok((void __user *)(unsigned long)mem->userspace_addr,
This should sanity check private_offset for private memslots. At a bare minimum, wrapping should be disallowed.
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mem->memory_size)) return -EINVAL; if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)@@ -1957,6 +1968,9 @@ int __kvm_set_memory_region(struct kvm *kvm, if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages) return -EINVAL; } else { /* Modify an existing slot. */ + /* Private memslots are immutable, they can only be deleted. */ + if (mem->flags & KVM_MEM_PRIVATE) + return -EINVAL;
These sanity checks belong in "KVM: Register private memslot to memory backing store", e.g. that patch is "broken" without the immutability restriction. It's somewhat moot because the code is unreachable, but it makes reviewing confusing/difficult. But rather than move the sanity checks back, I think I'd prefer to pull all of patch 10 here. I think it also makes sense to drop "KVM: Use memfile_pfn_ops to obtain pfn for private pages" and add the pointer in "struct kvm_memory_slot" in patch "KVM: Extend the memslot to support fd-based private memory", with the use of the ops folded into "KVM: Handle page fault for private memory". Adding code to KVM and KVM-x86 in a single patch is ok, and overall makes things easier to review because the new helpers have a user right away, especially since there will be #ifdeffery. I.e. end up with something like: mm: Introduce memfile_notifier mm/shmem: Restrict MFD_INACCESSIBLE memory against RLIMIT_MEMLOCK KVM: Extend the memslot to support fd-based private memory KVM: Use kvm_userspace_memory_region_ext KVM: Add KVM_EXIT_MEMORY_ERROR exit KVM: Handle page fault for private memory KVM: Register private memslot to memory backing store KVM: Zap existing KVM mappings when pages changed in the private fd KVM: Enable and expose KVM_MEM_PRIVATE
if ((mem->userspace_addr != old->userspace_addr) || (npages != old->npages) || ((mem->flags ^ old->flags) & KVM_MEM_READONLY)) -- 2.17.1