Re: [RFC PATCH 15/19] kvm: handle KVM_EXIT_MEMORY_FAULT

[Xiaoyao Li]

On 8/9/2023 11:02 PM, Xu Yilun wrote:
> On 2023-07-31 at 12:21:57 -0400, 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
> > gmem memory backend.
> >
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > ---
> >   accel/kvm/kvm-all.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 52 insertions(+)
> >
> > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> > index f9b5050b8885..72d50b923bf2 100644
> > --- a/accel/kvm/kvm-all.c
> > +++ b/accel/kvm/kvm-all.c
> > @@ -3040,6 +3040,48 @@ 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;
> > +    void *addr;
> > +    RAMBlock *rb;
> > +    ram_addr_t offset;
> > +    int ret = -1;
> > +
> > +    section = memory_region_find(get_system_memory(), start, size);
> > +    if (!section.mr) {
> > +        return ret;
> > +    }
> > +
> > +    if (memory_region_can_be_private(section.mr)) {
> > +        if (to_private) {
> > +            ret = kvm_set_memory_attributes_private(start, size);
> > +        } else {
> > +            ret = kvm_set_memory_attributes_shared(start, size);
> > +        }
> > +
> > +        if (ret) {
> > +            return ret;
>
> Should we unref the memory region before return?

Thanks for catching this!

> Thanks,
> Yilun
>
> > +        }
> > +
> > +        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");
> > +    }
> > +
> > +    memory_region_unref(section.mr);
> > +    return ret;
> > +}