Re: [PATCH v3 09/70] physmem: Introduce ram_block_convert_range() for page conversion

[Xiaoyao Li]

On 11/18/2023 5:03 AM, Isaku Yamahata wrote:
> On Wed, Nov 15, 2023 at 02:14:18AM -0500,
> Xiaoyao Li <xiaoyao.li@intel.com> wrote:
>
> > It's used for discarding opposite memory after memory conversion, for
> > confidential guest.
> >
> > When page is converted from shared to private, the original shared
> > memory can be discarded via ram_block_discard_range();
> >
> > When page is converted from private to shared, the original private
> > memory is back'ed by guest_memfd. Introduce
> > ram_block_discard_guest_memfd_range() for discarding memory in
> > guest_memfd.
> >
> > Originally-from: Isaku Yamahata <isaku.yamahata@intel.com>
> > Codeveloped-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > ---
> >   include/exec/cpu-common.h |  2 ++
> >   system/physmem.c          | 50 +++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 52 insertions(+)
> >
> > diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
> > index 41115d891940..de728a18eef2 100644
> > --- a/include/exec/cpu-common.h
> > +++ b/include/exec/cpu-common.h
> > @@ -175,6 +175,8 @@ typedef int (RAMBlockIterFunc)(RAMBlock *rb, void *opaque);
> >   
> >   int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque);
> >   int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length);
> > +int ram_block_convert_range(RAMBlock *rb, uint64_t start, size_t length,
> > +                            bool shared_to_private);
> >   
> >   #endif
> >   
> > diff --git a/system/physmem.c b/system/physmem.c
> > index ddfecddefcd6..cd6008fa09ad 100644
> > --- a/system/physmem.c
> > +++ b/system/physmem.c
> > @@ -3641,6 +3641,29 @@ err:
> >       return ret;
> >   }
> >   
> > +static int ram_block_discard_guest_memfd_range(RAMBlock *rb, uint64_t start,
> > +                                               size_t length)
> > +{
> > +    int ret = -1;
> > +
> > +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
> > +    ret = fallocate(rb->guest_memfd, FALLOC_FL_PUNCH_HOLE | 
> > FALLOC_FL_KEEP_SIZE,
> > +                    start, length);
> > +
> > +    if (ret) {
> > +        ret = -errno;
> > +        error_report("%s: Failed to fallocate %s:%" PRIx64 " +%zx (%d)",
> > +                     __func__, rb->idstr, start, length, ret);
> > +    }
> > +#else
> > +    ret = -ENOSYS;
> > +    error_report("%s: fallocate not available %s:%" PRIx64 " +%zx (%d)",
> > +                 __func__, rb->idstr, start, length, ret);
> > +#endif
> > +
> > +    return ret;
> > +}
> > +
> >   bool ramblock_is_pmem(RAMBlock *rb)
> >   {
> >       return rb->flags & RAM_PMEM;
> > @@ -3828,3 +3851,30 @@ bool ram_block_discard_is_required(void)
> >       return qatomic_read(&ram_block_discard_required_cnt) ||
> >              qatomic_read(&ram_block_coordinated_discard_required_cnt);
> >   }
> > +
> > +int ram_block_convert_range(RAMBlock *rb, uint64_t start, size_t length,
> > +                            bool shared_to_private)
> > +{
> > +    if (!rb || rb->guest_memfd < 0) {
> > +        return -1;
> > +    }
> > +
> > +    if (!QEMU_PTR_IS_ALIGNED(start, qemu_host_page_size) ||
> > +        !QEMU_PTR_IS_ALIGNED(length, qemu_host_page_size)) {
> > +        return -1;
> > +    }
> > +
> > +    if (!length) {
> > +        return -1;
> > +    }
> > +
> > +    if (start + length > rb->max_length) {
> > +        return -1;
> > +    }
> > +
> > +    if (shared_to_private) {
> > +        return ram_block_discard_range(rb, start, length);
> > +    } else {
> > +        return ram_block_discard_guest_memfd_range(rb, start, length);
> > +    }
> > +}
>
> Originally this function issued KVM_SET_MEMORY_ATTRIBUTES, the function name
> mad sense. But now it doesn't, and it issues only punch hole. We should rename
> it to represent what it actually does. discard_range?

ram_block_discard_range() already exists for non-guest-memfd memory discard.

I cannot come up with a proper name. e.g., 
ram_block_discard_opposite_range() while *opposite* seems unclear.

Do you have any better idea?