Re: [Qemu-devel] [PATCH] exec.c: Ensure right alignment also for file backed ram

[Dominik Dingel]

On Fri, 29 Apr 2016 15:32:22 +0800
Fam Zheng <address@hidden> wrote:

> On Mon, 04/25 13:55, Dominik Dingel wrote:
> > While in the anonymous ram case we already take care of the right alignment
> > such an alignment gurantee does not exist for file backed ram allocation.
> 
> s/gurantee/guarantee/
> 
> Otherwise looks good to me,
> 
> Reviewed-by: Fam Zheng <address@hidden>

Thank you very much!

Paolo do you want me to fix the typo, add the r-b and resend the patch?

> > 
> > Instead, pagesize is used for alignment. On s390 this is not enough for 
> > gmap,
> > as we need to satisfy an alignment up to segments.
> > 
> > Reported-by: Halil Pasic <address@hidden>
> > Signed-off-by: Dominik Dingel <address@hidden>
> > 
> > ---
> > 
> > v2 -> v3:
> > Skipping additional variable and just use alignment of memory region.
> > As memory will not be backpropagated it is enough to round up to page_sizes.
> > 
> > v1 -> v2:
> > While enforcing alignments we allow memory sizes on page_size.
> > On mmap the memory size will be round up to alignments.
> > 
> > I thought about moving this alignment into qemu_ram_mmap but the result
> > was a lot of code churn, the other possibility was to create an additional
> > define ending up with two defines with the same semantics.
> > ---
> >  exec.c               |  5 +++--
> >  include/qemu/osdep.h | 13 +++++++++++++
> >  util/oslib-posix.c   | 13 -------------
> >  3 files changed, 16 insertions(+), 15 deletions(-)
> > 
> > diff --git a/exec.c b/exec.c
> > index c4f9036..fc75266 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -1296,7 +1296,7 @@ static void *file_ram_alloc(RAMBlock *block,
> >      }
> >  
> >      page_size = qemu_fd_getpagesize(fd);
> > -    block->mr->align = page_size;
> > +    block->mr->align = MAX(page_size, QEMU_VMALLOC_ALIGN);
> >  
> >      if (memory < page_size) {
> >          error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal to "
> > @@ -1317,7 +1317,8 @@ static void *file_ram_alloc(RAMBlock *block,
> >          perror("ftruncate");
> >      }
> >  
> > -    area = qemu_ram_mmap(fd, memory, page_size, block->flags & RAM_SHARED);
> > +    area = qemu_ram_mmap(fd, memory, block->mr->align,
> > +                         block->flags & RAM_SHARED);
> >      if (area == MAP_FAILED) {
> >          error_setg_errno(errp, errno,
> >                           "unable to map backing store for guest RAM");
> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > index 408783f..783270f 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -247,6 +247,19 @@ void qemu_anon_ram_free(void *ptr, size_t size);
> >  
> >  #endif
> >  
> > +#if defined(__linux__) && \
> > +    (defined(__x86_64__) || defined(__arm__) || defined(__aarch64__))
> > +   /* Use 2 MiB alignment so transparent hugepages can be used by KVM.
> > +      Valgrind does not support alignments larger than 1 MiB,
> > +      therefore we need special code which handles running on Valgrind. */
> > +#  define QEMU_VMALLOC_ALIGN (512 * 4096)
> > +#elif defined(__linux__) && defined(__s390x__)
> > +   /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
> > +#  define QEMU_VMALLOC_ALIGN (256 * 4096)
> > +#else
> > +#  define QEMU_VMALLOC_ALIGN getpagesize()
> > +#endif
> > +
> >  int qemu_madvise(void *addr, size_t len, int advice);
> >  
> >  int qemu_open(const char *name, int flags, ...);
> > diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> > index 6cc4b8f..4adde93 100644
> > --- a/util/oslib-posix.c
> > +++ b/util/oslib-posix.c
> > @@ -26,19 +26,6 @@
> >   * THE SOFTWARE.
> >   */
> >  
> > -#if defined(__linux__) && \
> > -    (defined(__x86_64__) || defined(__arm__) || defined(__aarch64__))
> > -   /* Use 2 MiB alignment so transparent hugepages can be used by KVM.
> > -      Valgrind does not support alignments larger than 1 MiB,
> > -      therefore we need special code which handles running on Valgrind. */
> > -#  define QEMU_VMALLOC_ALIGN (512 * 4096)
> > -#elif defined(__linux__) && defined(__s390x__)
> > -   /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
> > -#  define QEMU_VMALLOC_ALIGN (256 * 4096)
> > -#else
> > -#  define QEMU_VMALLOC_ALIGN getpagesize()
> > -#endif
> > -
> >  #include "qemu/osdep.h"
> >  #include <termios.h>
> >  #include <termios.h>
> > -- 
> > 2.6.6
> > 
> > 
>