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

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

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@xxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxx>
> > Co-developed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > ---
> >   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