On Tue, Jan 17, 2023 at 07:35:58PM +0000, Sean Christopherson wrote: > On Tue, Jan 17, 2023, Chao Peng wrote: > > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote: > > > On Fri, Dec 02, 2022, Chao Peng wrote: > > > > @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > > > > > > > > if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu)) > > > > static_call(kvm_x86_update_cpu_dirty_logging)(vcpu); > > > > + > > > > + if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) { > > > > + vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN; > > > > > > Synthesizing triple fault shutdown is not the right approach. Even with TDX's > > > MCE "architecture" (heavy sarcasm), it's possible that host userspace and the > > > guest have a paravirt interface for handling memory errors without killing the > > > host. > > > > Agree shutdown is not the correct choice. I see you made below change: > > > > send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva, PAGE_SHIFT, current) > > > > The MCE may happen in any thread than KVM thread, sending siginal to > > 'current' thread may not be the expected behavior. > > This is already true today, e.g. a #MC in memory that is mapped into the guest can > be triggered by a host access. Hrm, but in this case we actually have a KVM > instance, and we know that the #MC is relevant to the KVM instance, so I agree > that signaling 'current' is kludgy. > > > Also how userspace can tell is the MCE on the shared page or private page? > > Do we care? > > We care. I was originally thinking we could require userspace to keep track of > things, but that's quite prescriptive and flawed, e.g. could race with conversions. > > One option would be to KVM_EXIT_MEMORY_FAULT, and then wire up a generic (not x86 > specific) KVM request to exit to userspace, e.g. > > /* KVM_EXIT_MEMORY_FAULT */ > struct { > #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 3) > #define KVM_MEMORY_EXIT_FLAG_HW_ERROR (1ULL << 4) > __u64 flags; > __u64 gpa; > __u64 size; > } memory; > > But I'm not sure that's the correct approach. It kinda feels like we're reinventing > the wheel. It seems like restrictedmem_get_page() _must_ be able to reject attempts > to get a poisoned page, i.e. restrictedmem_get_page() should yield KVM_PFN_ERR_HWPOISON. Yes, I see there is -EHWPOISON handling for hva_to_pfn() for shared memory. It makes sense doing similar for private page. > Assuming that's the case, then I believe KVM simply needs to zap SPTEs in response > to an error notification in order to force vCPUs to fault on the poisoned page. Agree, this is waht we should do anyway. > > > > > + return -EINVAL; > > > > if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM) > > > > return -EINVAL; > > > > if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr) > > > > @@ -2020,6 +2154,9 @@ 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. */ > > > > > > I'm 99% certain I suggested this, but if we're going to make these memslots > > > immutable, then we should straight up disallow dirty logging, otherwise we'll > > > end up with a bizarre uAPI. > > > > But in my mind dirty logging will be needed in the very short time, when > > live migration gets supported? > > Ya, but if/when live migration support is added, private memslots will no longer > be immutable as userspace will want to enable dirty logging only when a VM is > being migrated, i.e. something will need to change. > > Given that it looks like we have clear line of sight to SEV+UPM guests, my > preference would be to allow toggling dirty logging from the get-go. It doesn't > necessarily have to be in the first patch, e.g. KVM could initially reject > KVM_MEM_LOG_DIRTY_PAGES + KVM_MEM_PRIVATE and then add support separately to make > the series easier to review, test, and bisect. > > static int check_memory_region_flags(struct kvm *kvm, > const struct kvm_userspace_memory_region2 *mem) > { > u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES; > > if (kvm_arch_has_private_mem(kvm) && > ~(mem->flags & KVM_MEM_LOG_DIRTY_PAGES)) > valid_flags |= KVM_MEM_PRIVATE; Adding this limitation is OK to me. It's not too hard to remove it when live migration gets added. > > > ... > } > > > > > + if (mem->flags & KVM_MEM_PRIVATE) > > > > + return -EINVAL; > > > > if ((mem->userspace_addr != old->userspace_addr) || > > > > (npages != old->npages) || > > > > ((mem->flags ^ old->flags) & KVM_MEM_READONLY)) > > > > @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm, > > > > new->npages = npages; > > > > new->flags = mem->flags; > > > > new->userspace_addr = mem->userspace_addr; > > > > + if (mem->flags & KVM_MEM_PRIVATE) { > > > > + new->restricted_file = fget(mem->restricted_fd); > > > > + if (!new->restricted_file || > > > > + !file_is_restrictedmem(new->restricted_file)) { > > > > + r = -EINVAL; > > > > + goto out; > > > > + } > > > > + new->restricted_offset = mem->restricted_offset; > > > > I see you changed slot->restricted_offset type from loff_t to gfn_t and > > used pgoff_t when doing the restrictedmem_bind/unbind(). Using page > > index is reasonable KVM internally and sounds simpler than loff_t. But > > we also need initialize it to page index here as well as changes in > > another two cases. This is needed when restricted_offset != 0. > > Oof. I'm pretty sure I completely missed that loff_t is used for byte offsets, > whereas pgoff_t is a frame index. > > Given that the restrictmem APIs take pgoff_t, I definitely think it makes sense > to the index, but I'm very tempted to store pgoff_t instead of gfn_t, and name > the field "index" to help connect the dots to the rest of kernel, where "pgoff_t index" > is quite common. > > And looking at those bits again, we should wrap all of the restrictedmem fields > with CONFIG_KVM_PRIVATE_MEM. It'll require minor tweaks to __kvm_set_memory_region(), > but I think will yield cleaner code (and internal APIs) overall. > > And wrap the three fields in an anonymous struct? E.g. this is a little more > versbose (restrictedmem instead restricted), but at first glance it doesn't seem > to cause widespared line length issues. > > #ifdef CONFIG_KVM_PRIVATE_MEM > struct { > struct file *file; > pgoff_t index; > struct restrictedmem_notifier notifier; > } restrictedmem; > #endif Looks better. Thanks, Chao > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 547b92215002..49e375e78f30 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -2364,8 +2364,7 @@ static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot, > > gfn_t gfn, kvm_pfn_t *pfn, > > int *order) > > { > > - pgoff_t index = gfn - slot->base_gfn + > > - (slot->restricted_offset >> PAGE_SHIFT); > > + pgoff_t index = gfn - slot->base_gfn + slot->restricted_offset; > > struct page *page; > > int ret; > > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 01db35ddd5b3..7439bdcb0d04 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -935,7 +935,7 @@ static bool restrictedmem_range_is_valid(struct kvm_memory_slot *slot, > > pgoff_t start, pgoff_t end, > > gfn_t *gfn_start, gfn_t *gfn_end) > > { > > - unsigned long base_pgoff = slot->restricted_offset >> PAGE_SHIFT; > > + unsigned long base_pgoff = slot->restricted_offset; > > > > if (start > base_pgoff) > > *gfn_start = slot->base_gfn + start - base_pgoff; > > @@ -2275,7 +2275,7 @@ int __kvm_set_memory_region(struct kvm *kvm, > > r = -EINVAL; > > goto out; > > } > > - new->restricted_offset = mem->restricted_offset; > > + new->restricted_offset = mem->restricted_offset >> PAGE_SHIFT; > > } > > > > r = kvm_set_memslot(kvm, old, new, change); > > > > Chao > > > > + } > > > > + > > > > + new->kvm = kvm; > > > > > > Set this above, just so that the code flows better.