| Message ID | 20240423150951.41600-56-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [PULL,01/63] meson: do not link pixman automatically into all targets | expand |
On Tue, 23 Apr 2024 at 16:16, Paolo Bonzini <pbonzini@redhat.com> wrote: > > From: Chao Peng <chao.p.peng@linux.intel.com> > > Upon an KVM_EXIT_MEMORY_FAULT exit, userspace needs to do the memory > conversion on the RAMBlock to turn the memory into desired attribute, > switching between private and shared. > > Currently only KVM_MEMORY_EXIT_FLAG_PRIVATE in flags is valid when > KVM_EXIT_MEMORY_FAULT happens. > > Note, KVM_EXIT_MEMORY_FAULT makes sense only when the RAMBlock has > guest_memfd memory backend. > > Note, KVM_EXIT_MEMORY_FAULT returns with -EFAULT, so special handling is > added. > > When page is converted from shared to private, the original shared > memory can be discarded via ram_block_discard_range(). Note, shared > memory can be discarded only when it's not back'ed by hugetlb because > hugetlb is supposed to be pre-allocated and no need for discarding. > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com> > Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com> > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com> > > Message-ID: <20240320083945.991426-13-michael.roth@amd.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Hi; Coverity points out an issue with this code (CID 1544114): > +int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private) > +{ > + MemoryRegionSection section; > + ram_addr_t offset; offset here is not initialized... > + MemoryRegion *mr; > + RAMBlock *rb; > + void *addr; > + int ret = -1; > + > + trace_kvm_convert_memory(start, size, to_private ? "shared_to_private" : "private_to_shared"); > + > + if (!QEMU_PTR_IS_ALIGNED(start, qemu_real_host_page_size()) || > + !QEMU_PTR_IS_ALIGNED(size, qemu_real_host_page_size())) { > + return -1; > + } > + > + if (!size) { > + return -1; > + } > + > + section = memory_region_find(get_system_memory(), start, size); > + mr = section.mr; > + if (!mr) { > + return -1; > + } > + > + if (!memory_region_has_guest_memfd(mr)) { > + error_report("Converting non guest_memfd backed memory region " > + "(0x%"HWADDR_PRIx" ,+ 0x%"HWADDR_PRIx") to %s", > + start, size, to_private ? "private" : "shared"); > + goto out_unref; > + } > + > + if (to_private) { > + ret = kvm_set_memory_attributes_private(start, size); > + } else { > + ret = kvm_set_memory_attributes_shared(start, size); > + } > + if (ret) { > + goto out_unref; > + } > + > + addr = memory_region_get_ram_ptr(mr) + section.offset_within_region; > + rb = qemu_ram_block_from_host(addr, false, &offset); ...and this call to qemu_ram_block_from_host() will only initialize offset if it does not fail (i.e. doesn't return NULL)... > + > + if (to_private) { > + if (rb->page_size != qemu_real_host_page_size()) { ...but here we assume rb is not NULL... > + /* > + * shared memory is backed by hugetlb, which is supposed to be > + * pre-allocated and doesn't need to be discarded > + */ > + goto out_unref; > + } > + ret = ram_block_discard_range(rb, offset, size); > + } else { > + ret = ram_block_discard_guest_memfd_range(rb, offset, size); ...and here we use offset assuming it has been initialized. I think this code should either handle the case where qemu_ram_block_from_host() fails, or, if it is impossible for it to fail in this situation, add an assert() and a comment about why we know it can't fail. > + } > + > +out_unref: > + memory_region_unref(mr); > + return ret; > +} thanks -- PMM
On Fri, Apr 26, 2024 at 3:40 PM Peter Maydell <peter.maydell@linaro.org> wrote: > > + addr = memory_region_get_ram_ptr(mr) + section.offset_within_region; > > + rb = qemu_ram_block_from_host(addr, false, &offset); > > ...and this call to qemu_ram_block_from_host() will only initialize > offset if it does not fail (i.e. doesn't return NULL)... > > I think this code should either handle the case where > qemu_ram_block_from_host() fails, or, if it is impossible > for it to fail in this situation, add an assert() and a > comment about why we know it can't fail. The assertion is in memory_region_get_ram_ptr(), but Coverity understandably cannot see it. Similar to other code in hw/virtio/virtio-balloon.c, this code is using memory_region_get_ram_ptr() as a roundabout way to go from MemoryRegion (in this case MemoryRegionSection) to RAMBlock. The right fix is to introduce memory_region_get_ram_block() and use it. Paolo
diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h index 217f3fe17ba..47f9e8be1b3 100644 --- a/include/sysemu/kvm.h +++ b/include/sysemu/kvm.h @@ -542,4 +542,6 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp); int kvm_set_memory_attributes_private(hwaddr start, uint64_t size); int kvm_set_memory_attributes_shared(hwaddr start, uint64_t size); +int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private); + #endif diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index f49b2b95b54..9eef2c64003 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -2900,6 +2900,69 @@ static void kvm_eat_signals(CPUState *cpu) } while (sigismember(&chkset, SIG_IPI)); } +int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private) +{ + MemoryRegionSection section; + ram_addr_t offset; + MemoryRegion *mr; + RAMBlock *rb; + void *addr; + int ret = -1; + + trace_kvm_convert_memory(start, size, to_private ? "shared_to_private" : "private_to_shared"); + + if (!QEMU_PTR_IS_ALIGNED(start, qemu_real_host_page_size()) || + !QEMU_PTR_IS_ALIGNED(size, qemu_real_host_page_size())) { + return -1; + } + + if (!size) { + return -1; + } + + section = memory_region_find(get_system_memory(), start, size); + mr = section.mr; + if (!mr) { + return -1; + } + + if (!memory_region_has_guest_memfd(mr)) { + error_report("Converting non guest_memfd backed memory region " + "(0x%"HWADDR_PRIx" ,+ 0x%"HWADDR_PRIx") to %s", + start, size, to_private ? "private" : "shared"); + goto out_unref; + } + + if (to_private) { + ret = kvm_set_memory_attributes_private(start, size); + } else { + ret = kvm_set_memory_attributes_shared(start, size); + } + if (ret) { + goto out_unref; + } + + addr = memory_region_get_ram_ptr(mr) + section.offset_within_region; + rb = qemu_ram_block_from_host(addr, false, &offset); + + if (to_private) { + if (rb->page_size != qemu_real_host_page_size()) { + /* + * shared memory is backed by hugetlb, which is supposed to be + * pre-allocated and doesn't need to be discarded + */ + goto out_unref; + } + ret = ram_block_discard_range(rb, offset, size); + } else { + ret = ram_block_discard_guest_memfd_range(rb, offset, size); + } + +out_unref: + memory_region_unref(mr); + return ret; +} + int kvm_cpu_exec(CPUState *cpu) { struct kvm_run *run = cpu->kvm_run; @@ -2967,18 +3030,20 @@ int kvm_cpu_exec(CPUState *cpu) ret = EXCP_INTERRUPT; break; } - fprintf(stderr, "error: kvm run failed %s\n", - strerror(-run_ret)); + if (!(run_ret == -EFAULT && run->exit_reason == KVM_EXIT_MEMORY_FAULT)) { + fprintf(stderr, "error: kvm run failed %s\n", + strerror(-run_ret)); #ifdef TARGET_PPC - if (run_ret == -EBUSY) { - fprintf(stderr, - "This is probably because your SMT is enabled.\n" - "VCPU can only run on primary threads with all " - "secondary threads offline.\n"); - } + if (run_ret == -EBUSY) { + fprintf(stderr, + "This is probably because your SMT is enabled.\n" + "VCPU can only run on primary threads with all " + "secondary threads offline.\n"); + } #endif - ret = -1; - break; + ret = -1; + break; + } } trace_kvm_run_exit(cpu->cpu_index, run->exit_reason); @@ -3061,6 +3126,19 @@ int kvm_cpu_exec(CPUState *cpu) break; } break; + case KVM_EXIT_MEMORY_FAULT: + trace_kvm_memory_fault(run->memory_fault.gpa, + run->memory_fault.size, + run->memory_fault.flags); + if (run->memory_fault.flags & ~KVM_MEMORY_EXIT_FLAG_PRIVATE) { + error_report("KVM_EXIT_MEMORY_FAULT: Unknown flag 0x%" PRIx64, + (uint64_t)run->memory_fault.flags); + ret = -1; + break; + } + ret = kvm_convert_memory(run->memory_fault.gpa, run->memory_fault.size, + run->memory_fault.flags & KVM_MEMORY_EXIT_FLAG_PRIVATE); + break; default: ret = kvm_arch_handle_exit(cpu, run); break; diff --git a/accel/kvm/trace-events b/accel/kvm/trace-events index e8c52cb9e7a..681ccb667d6 100644 --- a/accel/kvm/trace-events +++ b/accel/kvm/trace-events @@ -31,3 +31,5 @@ kvm_cpu_exec(void) "" kvm_interrupt_exit_request(void) "" kvm_io_window_exit(void) "" kvm_run_exit_system_event(int cpu_index, uint32_t event_type) "cpu_index %d, system_even_type %"PRIu32 +kvm_convert_memory(uint64_t start, uint64_t size, const char *msg) "start 0x%" PRIx64 " size 0x%" PRIx64 " %s" +kvm_memory_fault(uint64_t start, uint64_t size, uint64_t flags) "start 0x%" PRIx64 " size 0x%" PRIx64 " flags 0x%" PRIx64