Re: [PATCH 0/2] cleanup on page size

[Wei Yang <richardw.yang@linux.intel.com>]

Hi, All,

I got one page size related question, hope to get some hint.

There is one comment in page_size_init().

    /* NOTE: we can always suppose that qemu_host_page_size >=
       TARGET_PAGE_SIZE */

The final result is true, since we compare qemu_host_page_size with
TARGET_PAGE_SIZE and if not qemu_host_page_size will be assigned to
TARGET_PAGE_SIZE.

Generally, there is no problem, but one corner case for migration.

In function ram_save_host_page(), it tries to save a whole host page. Or to be
specific, it tries to save a whole REAL host page.

The potential problem is when qemu_real_host_page_size < TARGET_PAGE_SIZE,
this whole host page would be a wrong range.

So I am wondering why we have the assumption written in page_size_init()?

I tried to dig out who and why we have this comment, but found the first
commit is

    commit 54936004fddc52c321cb3f9a9a51140e782bed5d
    Author: bellard <bellard@c046a42c-6fe2-441c-8c8c-71466251a162>
    Date:   Tue May 13 00:25:15 2003 +0000
    
        mmap emulation
    
    
        git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@158 c046a42c-6fe2-441c-8c8c-71466251a162

There is no reason logged.

On Sun, Oct 13, 2019 at 10:11:43AM +0800, Wei Yang wrote:
>Patch 1 simplify the definition of xxx_PAGE_ALIGN.
>Patch 2 replaces getpagesize() with qemu_real_host_page_size. This one touch a
>volume of code. If some point is not correct, I'd appreciate your
>notification.
>
>Wei Yang (2):
>  cpu: use ROUND_UP() to define xxx_PAGE_ALIGN
>  core: replace getpagesize() with qemu_real_host_page_size
>
> accel/kvm/kvm-all.c            |  6 +++---
> backends/hostmem.c             |  2 +-
> block.c                        |  4 ++--
> block/file-posix.c             |  9 +++++----
> block/io.c                     |  2 +-
> block/parallels.c              |  2 +-
> block/qcow2-cache.c            |  2 +-
> contrib/vhost-user-gpu/vugbm.c |  2 +-
> exec.c                         |  6 +++---
> hw/intc/s390_flic_kvm.c        |  2 +-
> hw/ppc/mac_newworld.c          |  2 +-
> hw/ppc/spapr_pci.c             |  2 +-
> hw/rdma/vmw/pvrdma_main.c      |  2 +-
> hw/vfio/spapr.c                |  7 ++++---
> include/exec/cpu-all.h         |  7 +++----
> include/exec/ram_addr.h        |  2 +-
> include/qemu/osdep.h           |  4 ++--
> migration/migration.c          |  2 +-
> migration/postcopy-ram.c       |  4 ++--
> monitor/misc.c                 |  2 +-
> target/ppc/kvm.c               |  2 +-
> tests/vhost-user-bridge.c      |  8 ++++----
> util/mmap-alloc.c              | 10 +++++-----
> util/oslib-posix.c             |  4 ++--
> util/oslib-win32.c             |  2 +-
> util/vfio-helpers.c            | 12 ++++++------
> 26 files changed, 55 insertions(+), 54 deletions(-)
>
>-- 
>2.17.1

-- 
Wei Yang
Help you, Help me