Re: [PATCH v3 10/70] kvm: handle KVM_EXIT_MEMORY_FAULT

Xiaoyao Li
2023-11-16T05:16:55Z

On 11/15/2023 6:42 PM, Daniel P. Berrangé wrote:
> On Wed, Nov 15, 2023 at 02:14:19AM -0500, Xiaoyao Li wrote:
>> From: Chao Peng <chao.p.peng@linux.intel.com>
>>
>> Currently only KVM_MEMORY_EXIT_FLAG_PRIVATE in flags is valid when
>> KVM_EXIT_MEMORY_FAULT happens. It indicates userspace needs to do
>> the memory conversion on the RAMBlock to turn the memory into desired
>> attribute, i.e., private/shared.
>>
>> 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.
>>
>> 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>
>> ---
>> accel/kvm/kvm-all.c | 76 +++++++++++++++++++++++++++++++++++++++------
>> 1 file changed, 66 insertions(+), 10 deletions(-)
>>
>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
>> index 76e2404d54d2..58abbcb6926e 100644
>> --- a/accel/kvm/kvm-all.c
>> +++ b/accel/kvm/kvm-all.c
>> @@ -2902,6 +2902,50 @@ static void kvm_eat_signals(CPUState *cpu)
>> } while (sigismember(&chkset, SIG_IPI));
>> }
>>
>> +static int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
>> +{
>> + MemoryRegionSection section;
>> + ram_addr_t offset;
>> + RAMBlock *rb;
>> + void *addr;
>> + int ret = -1;
>> +
>> + section = memory_region_find(get_system_memory(), start, size);
>> + if (!section.mr) {
>> + return ret;
>> + }
>> +
>> + if (memory_region_has_guest_memfd(section.mr)) {
>> + if (to_private) {
>> + ret = kvm_set_memory_attributes_private(start, size);
>> + } else {
>> + ret = kvm_set_memory_attributes_shared(start, size);
>> + }
>> +
>> + if (ret) {
>> + memory_region_unref(section.mr);
>> + return ret;
>> + }
>> +
>> + addr = memory_region_get_ram_ptr(section.mr) +
>> + section.offset_within_region;
>> + rb = qemu_ram_block_from_host(addr, false, &offset);
>> + /*
>> + * With KVM_SET_MEMORY_ATTRIBUTES by kvm_set_memory_attributes(),
>> + * operation on underlying file descriptor is only for releasing
>> + * unnecessary pages.
>> + */
>> + ram_block_convert_range(rb, offset, size, to_private);
>> + } else {
>> + warn_report("Convert non guest_memfd backed memory region "
>> + "(0x%"HWADDR_PRIx" ,+ 0x%"HWADDR_PRIx") to %s",
>> + start, size, to_private ? "private" : "shared");
>
> Again, if you're returning '-1' to indicate error, then
> using warn_report is wrong, it should be error_report.
>
> warn_report is for when you return success, indicating
> the problem was non-fatal.

Learned.

Thanks!

>> + }
>> +
>> + memory_region_unref(section.mr);
>> + return ret;
>> +}
>> +
>> int kvm_cpu_exec(CPUState *cpu)
>> {
>> struct kvm_run *run = cpu->kvm_run;
>> @@ -2969,18 +3013,20 @@ 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);
>> @@ -3067,6 +3113,16 @@ int kvm_cpu_exec(CPUState *cpu)
>> break;
>> }
>> break;
>> + case KVM_EXIT_MEMORY_FAULT:
>> + 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:
>> DPRINTF("kvm_arch_handle_exit\n");
>> ret = kvm_arch_handle_exit(cpu, run);
>> --
>> 2.34.1
>>
>
> With regards,
> Daniel