On 2018-12-18 at 08:52:09 -0500, Michael S. Tsirkin wrote:
> On Tue, Dec 18, 2018 at 04:17:12PM +0800, Zhang Yi wrote:
> > When a file supporting DAX is used as vNVDIMM backend, mmap it with
> > MAP_SYNC flag in addition can guarantee the persistence of guest write
> > to the backend file without other QEMU actions (e.g., periodic fsync()
> > by QEMU).
> >
> > A set of RAM_SYNC flags are added to qemu_ram_mmap():
> >
> > Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com>
> > Signed-off-by: Zhang Yi <yi.z.zh...@linux.intel.com>
>
> Should we be reusing RAM_ flags? These are used widely
> already -are you going to allow RAM_SYNC everywhere
> where other RAM flags are legal?
> E.g. memory_region_init_ram_from_file?
To reuse the RAM_* is much straightforward, just like RAM_SHARE, it is a
mmmap flag, and we will check the inlegal flags at a easy way.
assert((ram_flags & ~(RAM_SHARED | RAM_PMEM | RAM_SYNC)) == 0);
What do you think, do you have a better choice? Thanks, Micheal.
>
>
> > ---
> > exec.c | 2 +-
> > include/exec/memory.h | 3 +++
> > include/exec/ram_addr.h | 1 +
> > include/qemu/mmap-alloc.h | 1 +
> > include/qemu/osdep.h | 29 +++++++++++++++++++++++++++++
> > util/mmap-alloc.c | 14 ++++++++++----
> > 6 files changed, 45 insertions(+), 5 deletions(-)
> >
> > diff --git a/exec.c b/exec.c
> > index e92a7da..dc4d180 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -2241,7 +2241,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size,
> > MemoryRegion *mr,
> > int64_t file_size;
> >
> > /* Just support these ram flags by now. */
> > - assert((ram_flags & ~(RAM_SHARED | RAM_PMEM)) == 0);
> > + assert((ram_flags & ~(RAM_SHARED | RAM_PMEM | RAM_SYNC)) == 0);
> >
> > if (xen_enabled()) {
> > error_setg(errp, "-mem-path not supported with Xen");
> > diff --git a/include/exec/memory.h b/include/exec/memory.h
> > index 667466b..33a4e2c 100644
> > --- a/include/exec/memory.h
> > +++ b/include/exec/memory.h
> > @@ -126,6 +126,9 @@ typedef struct IOMMUNotifier IOMMUNotifier;
> > /* RAM is a persistent kind memory */
> > #define RAM_PMEM (1 << 5)
> >
> > +/* RAM can be mmap by a MAP_SYNC flag */
>
> "RAM is mmap-ed with MAP_SYNC"
>
> > +#define RAM_SYNC (1 << 6)
> > +
> > static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
> > IOMMUNotifierFlag flags,
> > hwaddr start, hwaddr end,
>
>
>
>
>
> > diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> > index 9ecd911..d239ce7 100644
> > --- a/include/exec/ram_addr.h
> > +++ b/include/exec/ram_addr.h
> > @@ -87,6 +87,7 @@ long qemu_getrampagesize(void);
> > * or bit-or of following values
> > * - RAM_SHARED: mmap the backing file or device with
> > MAP_SHARED
> > * - RAM_PMEM: the backend @mem_path or @fd is persistent
> > memory
> > + * - RAM_SYNC: mmap with MAP_SYNC flag
> > * Other bits are ignored.
> > * @mem_path or @fd: specify the backing file or device
> > * @errp: pointer to Error*, to store an error if it happens
> > diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> > index 6fe6ed4..1755a8b 100644
> > --- a/include/qemu/mmap-alloc.h
> > +++ b/include/qemu/mmap-alloc.h
> > @@ -18,6 +18,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
> > * @flags: specifies additional properties of the mapping, which can be
> > one or
> > * bit-or of following values
> > * - RAM_SHARED: mmap with MAP_SHARED flag
> > + * - RAM_SYNC: mmap with MAP_SYNC flag
> > * Other bits are ignored.
> > *
> > * Return:
> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > index 3bf48bc..f94ea68 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -410,6 +410,35 @@ void qemu_anon_ram_free(void *ptr, size_t size);
> > # define QEMU_VMALLOC_ALIGN getpagesize()
> > #endif
> >
> > +/*
> > + * MAP_SHARED_VALIDATE and MAP_SYNC are introduced in Linux kernel
> > + * 4.15, so they may not be defined when compiling on older kernels.
>
> Then you want to import the relevant headers into linux-headers
> using scripts/update-linux-headers.sh. Pls do not duplicate code.
Indeed, will update it.
>
> > + */
> > +#ifdef CONFIG_LINUX
> > +
> > +#include <sys/mman.h>
> > +
> > +#ifndef MAP_SHARED_VALIDATE
> > +#define MAP_SHARED_VALIDATE 0x3
> > +#endif
> > +
> > +#ifndef MAP_SYNC
> > +#define MAP_SYNC 0x80000
> > +#endif
> > +
> > +/* MAP_SYNC is only available with MAP_SHARED_VALIDATE. */
> > +#define MAP_SYNC_FLAGS (MAP_SYNC | MAP_SHARED_VALIDATE)
>
> Given mmap flags tend to start with MAP_, adding our own ones
> unconditionally is not a good idea.
How about to move the define to other place?
>
>
> > +
> > +#else /* !CONFIG_LINUX */
> > +
> > +#define MAP_SHARED_VALIDATE 0x0
> > +#define MAP_SYNC 0x0
> > +
> > +#define QEMU_HAS_MAP_SYNC false
>
> Isn't just checking MAP_SYNC enough?
>
> > +#define MAP_SYNC_FLAGS 0
> > +
> > +#endif /* CONFIG_LINUX */
> > +
> > #ifdef CONFIG_POSIX
> > struct qemu_signalfd_siginfo {
> > uint32_t ssi_signo; /* Signal number */
> > diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> > index 8f0a740..89ae862 100644
> > --- a/util/mmap-alloc.c
> > +++ b/util/mmap-alloc.c
> > @@ -99,6 +99,8 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
> > uint32_t flags)
> > void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1,
> > 0);
> > #endif
> > bool shared = flags & RAM_SHARED;
> > + bool is_pmem = flags & RAM_PMEM;
> > + int mmap_xflags = 0;
> > size_t offset;
> > void *ptr1;
> >
> > @@ -109,16 +111,20 @@ void *qemu_ram_mmap(int fd, size_t size, size_t
> > align, uint32_t flags)
> > assert(is_power_of_2(align));
> > /* Always align to host page size */
> > assert(align >= getpagesize());
> > + if ((flags & RAM_SYNC) && shared && is_pmem) {
> > + mmap_xflags |= MAP_SYNC_FLAGS;
> > + }
> >
> > offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
> > + retry_mmap_fd:
> > ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
> > MAP_FIXED |
> > (fd == -1 ? MAP_ANONYMOUS : 0) |
> > - (shared ? MAP_SHARED : MAP_PRIVATE),
> > + (shared ? MAP_SHARED : MAP_PRIVATE) | mmap_xflags,
> > fd, 0);
> > - if (ptr1 == MAP_FAILED) {
> > - munmap(ptr, total);
> > - return MAP_FAILED;
> > + if ((ptr1 == MAP_FAILED) && (mmap_xflags & MAP_SYNC_FLAGS)) {
> > + mmap_xflags &= ~MAP_SYNC_FLAGS;
> > + goto retry_mmap_fd;
> > }
> >
> > if (offset > 0) {
> > --
> > 2.7.4
