[PATCH for-6.0 v1 0/3] softmmu/physmem: shared anonymous memory fixes

[PATCH for-6.0 v1 0/3] softmmu/physmem: shared anonymous memory fixes

[David Hildenbrand]

Fixes related to shared anonymous memory, previously sent as part of
    https://lore.kernel.org/r/20210319101230.21531-1-david@redhat.com

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Kotrasinski <i.kotrasinsk@partner.samsung.com>
Cc: Richard Henderson <richard.henderson@linaro.org>

David Hildenbrand (3):
  softmmu/physmem: Mark shared anonymous memory RAM_SHARED
  softmmu/physmem: Fix ram_block_discard_range() to handle shared
    anonymous memory
  softmmu/physmem: Fix qemu_ram_remap() to handle shared anonymous
    memory

 softmmu/physmem.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)


base-commit: ee82c086baaa534d1af26cb8b86e86fb047af918
-- 
2.30.2

[PATCH for-6.0 v1 1/3] softmmu/physmem: Mark shared anonymous memory RAM_SHARED

[David Hildenbrand]

Let's drop the "shared" parameter from ram_block_add() and properly
store it in the flags of the ram block instead, such that
qemu_ram_is_shared() properly succeeds on all ram blocks that were mapped
MAP_SHARED.

We'll use this information next to fix some cases with shared anonymous
memory.

Reviewed-by: Igor Kotrasinski <i.kotrasinsk@partner.samsung.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 softmmu/physmem.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 85034d9c11..76bb8e324e 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1927,8 +1927,9 @@ static void dirty_memory_extend(ram_addr_t old_ram_size,
     }
 }
 
-static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
+static void ram_block_add(RAMBlock *new_block, Error **errp)
 {
+    const bool shared = qemu_ram_is_shared(new_block);
     RAMBlock *block;
     RAMBlock *last_block = NULL;
     ram_addr_t old_ram_size, new_ram_size;
@@ -2064,7 +2065,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
         return NULL;
     }
 
-    ram_block_add(new_block, &local_err, ram_flags & RAM_SHARED);
+    ram_block_add(new_block, &local_err);
     if (local_err) {
         g_free(new_block);
         error_propagate(errp, local_err);
@@ -2127,10 +2128,13 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
     if (host) {
         new_block->flags |= RAM_PREALLOC;
     }
+    if (share) {
+        new_block->flags |= RAM_SHARED;
+    }
     if (resizeable) {
         new_block->flags |= RAM_RESIZEABLE;
     }
-    ram_block_add(new_block, &local_err, share);
+    ram_block_add(new_block, &local_err);
     if (local_err) {
         g_free(new_block);
         error_propagate(errp, local_err);
-- 
2.30.2

[PATCH for-6.0 v1 2/3] softmmu/physmem: Fix ram_block_discard_range() to handle shared anonymous memory

[David Hildenbrand]

We can create shared anonymous memory via
    "-object memory-backend-ram,share=on,..."
which is, for example, required by PVRDMA for mremap() to work.

Shared anonymous memory is weird, though. Instead of MADV_DONTNEED, we
have to use MADV_REMOVE: MADV_DONTNEED will only remove / zap all
relevant page table entries of the current process, the backend storage
will not get removed, resulting in no reduced memory consumption and
a repopulation of previous content on next access.

Shared anonymous memory is internally really just shmem, but without a
fd exposed. As we cannot use fallocate() without the fd to discard the
backing storage, MADV_REMOVE gets the same job done without a fd as
documented in "man 2 madvise". Removing backing storage implicitly
invalidates all page table entries with relevant mappings - an additional
MADV_DONTNEED is not required.

Fixes: 06329ccecfa0 ("mem: add share parameter to memory-backend-ram")
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 softmmu/physmem.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 76bb8e324e..afff96a6dc 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3506,6 +3506,7 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
         /* The logic here is messy;
          *    madvise DONTNEED fails for hugepages
          *    fallocate works on hugepages and shmem
+         *    shared anonymous memory requires madvise REMOVE
          */
         need_madvise = (rb->page_size == qemu_host_page_size);
         need_fallocate = rb->fd != -1;
@@ -3539,7 +3540,11 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
              * fallocate'd away).
              */
 #if defined(CONFIG_MADVISE)
-            ret =  madvise(host_startaddr, length, MADV_DONTNEED);
+            if (qemu_ram_is_shared(rb) && rb->fd < 0) {
+                ret = madvise(host_startaddr, length, MADV_REMOVE);
+            } else {
+                ret = madvise(host_startaddr, length, MADV_DONTNEED);
+            }
             if (ret) {
                 ret = -errno;
                 error_report("ram_block_discard_range: Failed to discard range "
-- 
2.30.2

[PATCH for-6.0 v1 3/3] softmmu/physmem: Fix qemu_ram_remap() to handle shared anonymous memory

[David Hildenbrand]

RAM_SHARED now also properly indicates shared anonymous memory. Let's check
that flag for anonymous memory as well, to restore the proper mapping.

Fixes: 06329ccecfa0 ("mem: add share parameter to memory-backend-ram")
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 softmmu/physmem.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index afff96a6dc..cc59f05593 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -2222,13 +2222,13 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
                 abort();
             } else {
                 flags = MAP_FIXED;
+                flags |= block->flags & RAM_SHARED ?
+                         MAP_SHARED : MAP_PRIVATE;
                 if (block->fd >= 0) {
-                    flags |= (block->flags & RAM_SHARED ?
-                              MAP_SHARED : MAP_PRIVATE);
                     area = mmap(vaddr, length, PROT_READ | PROT_WRITE,
                                 flags, block->fd, offset);
                 } else {
-                    flags |= MAP_PRIVATE | MAP_ANONYMOUS;
+                    flags |= MAP_ANONYMOUS;
                     area = mmap(vaddr, length, PROT_READ | PROT_WRITE,
                                 flags, -1, 0);
                 }
-- 
2.30.2

Re: [PATCH for-6.0 v1 0/3] softmmu/physmem: shared anonymous memory fixes

[Peter Xu]

On Tue, Apr 06, 2021 at 10:01:23AM +0200, David Hildenbrand wrote:
> Fixes related to shared anonymous memory, previously sent as part of

The series looks good, but maybe 6.1 material? Since 06329ccecfa ("mem: add
share parameter to memory-backend-ram", 2018-02-19) is introduced in 2.12.

-- 
Peter Xu

Re: [PATCH for-6.0 v1 0/3] softmmu/physmem: shared anonymous memory fixes

[David Hildenbrand]

On 06.04.21 18:46, Peter Xu wrote:
> On Tue, Apr 06, 2021 at 10:01:23AM +0200, David Hildenbrand wrote:
>> Fixes related to shared anonymous memory, previously sent as part of
> 
> The series looks good, but maybe 6.1 material? Since 06329ccecfa ("mem: add
> share parameter to memory-backend-ram", 2018-02-19) is introduced in 2.12.

Thanks, but IIRC, there is no rule that requires bugfixes for fixes only 
introduced in this release.

"After the hard feature freeze, the master branch in git is no longer 
open for general development. Only bug fixes will be accepted until the 
next release."

-- 
Thanks,

David / dhildenb

Re: [PATCH for-6.0 v1 0/3] softmmu/physmem: shared anonymous memory fixes

[David Hildenbrand]

On 06.04.21 10:01, David Hildenbrand wrote:
> Fixes related to shared anonymous memory, previously sent as part of
>      https://lore.kernel.org/r/20210319101230.21531-1-david@redhat.com
> 

Peter, Eduardo, Michael, David, Paolo,

can someone please pick this up?

Thanks

> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Cc: Igor Kotrasinski <i.kotrasinsk@partner.samsung.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> 
> David Hildenbrand (3):
>    softmmu/physmem: Mark shared anonymous memory RAM_SHARED
>    softmmu/physmem: Fix ram_block_discard_range() to handle shared
>      anonymous memory
>    softmmu/physmem: Fix qemu_ram_remap() to handle shared anonymous
>      memory
> 
>   softmmu/physmem.c | 23 ++++++++++++++++-------
>   1 file changed, 16 insertions(+), 7 deletions(-)
> 
> 
> base-commit: ee82c086baaa534d1af26cb8b86e86fb047af918
> 


-- 
Thanks,

David / dhildenb