[Qemu-devel] [PATCH v2 0/2] memory: Convert skip_dump to ram_device and avoid memcpy

[Qemu-devel] [PATCH v2 0/2] memory: Convert skip_dump to ram_device and avoid memcpy

[Alex Williamson]

v2: retain ram_device flag to avoid extra cache miss, per Paolo.

Paolo, posting for completeness, I can merge through my tree if you
want to Ack.  Thanks,

Alex

---

Alex Williamson (2):
      memory: Replace skip_dump flag with "ram_device"
      memory: Don't use memcpy for ram_device regions


 hw/vfio/common.c      |    9 ++----
 hw/vfio/spapr.c       |    2 +
 include/exec/memory.h |   47 ++++++++++++++++++++---------
 memory.c              |   80 +++++++++++++++++++++++++++++++++++++++++++++++--
 memory_mapping.c      |    2 +
 trace-events          |    2 +
 6 files changed, 116 insertions(+), 26 deletions(-)

[Qemu-devel] [PATCH v2 1/2] memory: Replace skip_dump flag with "ram_device"

[Alex Williamson]

Setting skip_dump on a MemoryRegion allows us to modify one specific
code path, but the restriction we're trying to address encompasses
more than that.  If we have a RAM MemoryRegion backed by a physical
device, it not only restricts our ability to dump that region, but
also affects how we should manipulate it.  Here we recognize that
MemoryRegions do not change to sometimes allow dumps and other times
not, so we replace setting the skip_dump flag with a new initializer
so that we know exactly the type of region to which we're applying
this behavior.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 hw/vfio/common.c      |    9 ++++-----
 hw/vfio/spapr.c       |    2 +-
 include/exec/memory.h |   41 ++++++++++++++++++++++++++++-------------
 memory.c              |   13 +++++++++----
 memory_mapping.c      |    2 +-
 5 files changed, 43 insertions(+), 24 deletions(-)

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 9505fb3..c764cb3 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -724,12 +724,11 @@ int vfio_region_mmap(VFIORegion *region)
 
         name = g_strdup_printf("%s mmaps[%d]",
                                memory_region_name(region->mem), i);
-        memory_region_init_ram_ptr(&region->mmaps[i].mem,
-                                   memory_region_owner(region->mem),
-                                   name, region->mmaps[i].size,
-                                   region->mmaps[i].mmap);
+        memory_region_init_ram_device_ptr(&region->mmaps[i].mem,
+                                          memory_region_owner(region->mem),
+                                          name, region->mmaps[i].size,
+                                          region->mmaps[i].mmap);
         g_free(name);
-        memory_region_set_skip_dump(&region->mmaps[i].mem);
         memory_region_add_subregion(region->mem, region->mmaps[i].offset,
                                     &region->mmaps[i].mem);
 
diff --git a/hw/vfio/spapr.c b/hw/vfio/spapr.c
index 7443d34..4409bcc 100644
--- a/hw/vfio/spapr.c
+++ b/hw/vfio/spapr.c
@@ -25,7 +25,7 @@ static bool vfio_prereg_listener_skipped_section(MemoryRegionSection *section)
     }
 
     return !memory_region_is_ram(section->mr) ||
-            memory_region_is_skip_dump(section->mr);
+            memory_region_is_ram_device(section->mr);
 }
 
 static void *vfio_prereg_gpa_to_vaddr(MemoryRegionSection *section, hwaddr gpa)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 79ccaab..a75b8c3 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -209,7 +209,7 @@ struct MemoryRegion {
     void (*destructor)(MemoryRegion *mr);
     uint64_t align;
     bool terminates;
-    bool skip_dump;
+    bool ram_device;
     bool enabled;
     bool warning_printed; /* For reservations */
     uint8_t vga_logging_count;
@@ -449,6 +449,30 @@ void memory_region_init_ram_ptr(MemoryRegion *mr,
                                 void *ptr);
 
 /**
+ * memory_region_init_ram_device_ptr:  Initialize RAM device memory region from
+ *                                     a user-provided pointer.
+ *
+ * A RAM device represents a mapping to a physical device, such as to a PCI
+ * MMIO BAR of an vfio-pci assigned device.  The memory region may be mapped
+ * into the VM address space and access to the region will modify memory
+ * directly.  However, the memory region should not be included in a memory
+ * dump (device may not be enabled/mapped at the time of the dump), and
+ * operations incompatible with manipulating MMIO should be avoided.  Replaces
+ * skip_dump flag.
+ *
+ * @mr: the #MemoryRegion to be initialized.
+ * @owner: the object that tracks the region's reference count
+ * @name: the name of the region.
+ * @size: size of the region.
+ * @ptr: memory to be mapped; must contain at least @size bytes.
+ */
+void memory_region_init_ram_device_ptr(MemoryRegion *mr,
+                                       struct Object *owner,
+                                       const char *name,
+                                       uint64_t size,
+                                       void *ptr);
+
+/**
  * memory_region_init_alias: Initialize a memory region that aliases all or a
  *                           part of another memory region.
  *
@@ -574,22 +598,13 @@ static inline bool memory_region_is_ram(MemoryRegion *mr)
 }
 
 /**
- * memory_region_is_skip_dump: check whether a memory region should not be
- *                             dumped
- *
- * Returns %true is a memory region should not be dumped(e.g. VFIO BAR MMAP).
+ * memory_region_is_ram_device: check whether a memory region is a ram device
  *
- * @mr: the memory region being queried
- */
-bool memory_region_is_skip_dump(MemoryRegion *mr);
-
-/**
- * memory_region_set_skip_dump: Set skip_dump flag, dump will ignore this memory
- *                              region
+ * Returns %true is a memory region is a device backed ram region
  *
  * @mr: the memory region being queried
  */
-void memory_region_set_skip_dump(MemoryRegion *mr);
+bool memory_region_is_ram_device(MemoryRegion *mr);
 
 /**
  * memory_region_is_romd: check whether a memory region is in ROMD mode
diff --git a/memory.c b/memory.c
index edbc701..7ffcff1 100644
--- a/memory.c
+++ b/memory.c
@@ -1355,9 +1355,14 @@ void memory_region_init_ram_ptr(MemoryRegion *mr,
     mr->ram_block = qemu_ram_alloc_from_ptr(size, ptr, mr, &error_fatal);
 }
 
-void memory_region_set_skip_dump(MemoryRegion *mr)
+void memory_region_init_ram_device_ptr(MemoryRegion *mr,
+                                       Object *owner,
+                                       const char *name,
+                                       uint64_t size,
+                                       void *ptr)
 {
-    mr->skip_dump = true;
+    memory_region_init_ram_ptr(mr, owner, name, size, ptr);
+    mr->ram_device = true;
 }
 
 void memory_region_init_alias(MemoryRegion *mr,
@@ -1491,9 +1496,9 @@ const char *memory_region_name(const MemoryRegion *mr)
     return mr->name;
 }
 
-bool memory_region_is_skip_dump(MemoryRegion *mr)
+bool memory_region_is_ram_device(MemoryRegion *mr)
 {
-    return mr->skip_dump;
+    return mr->ram_device;
 }
 
 uint8_t memory_region_get_dirty_log_mask(MemoryRegion *mr)
diff --git a/memory_mapping.c b/memory_mapping.c
index e3e0d95..6a39d71 100644
--- a/memory_mapping.c
+++ b/memory_mapping.c
@@ -206,7 +206,7 @@ static void guest_phys_blocks_region_add(MemoryListener *listener,
 
     /* we only care about RAM */
     if (!memory_region_is_ram(section->mr) ||
-        memory_region_is_skip_dump(section->mr)) {
+        memory_region_is_ram_device(section->mr)) {
         return;
     }
 

[Qemu-devel] [PATCH v2 2/2] memory: Don't use memcpy for ram_device regions

[Alex Williamson]

With a vfio assigned device we lay down a base MemoryRegion registered
as an IO region, giving us read & write accessors.  If the region
supports mmap, we lay down a higher priority sub-region MemoryRegion
on top of the base layer initialized as a RAM device pointer to the
mmap.  Finally, if we have any quirks for the device (ie. address
ranges that need additional virtualization support), we put another IO
sub-region on top of the mmap MemoryRegion.  When this is flattened,
we now potentially have sub-page mmap MemoryRegions exposed which
cannot be directly mapped through KVM.

This is as expected, but a subtle detail of this is that we end up
with two different access mechanisms through QEMU.  If we disable the
mmap MemoryRegion, we make use of the IO MemoryRegion and service
accesses using pread and pwrite to the vfio device file descriptor.
If the mmap MemoryRegion is enabled and results in one of these
sub-page gaps, QEMU handles the access as RAM, using memcpy to the
mmap.  Using either pread/pwrite or the mmap directly should be
correct, but using memcpy causes us problems.  I expect that not only
does memcpy not necessarily honor the original width and alignment in
performing a copy, but it potentially also uses processor instructions
not intended for MMIO spaces.  It turns out that this has been a
problem for Realtek NIC assignment, which has such a quirk that
creates a sub-page mmap MemoryRegion access.

To resolve this, we disable memory_access_is_direct() for ram_device
regions since QEMU assumes that it can use memcpy for those regions.
Instead we access through MemoryRegionOps, which replaces the memcpy
with simple de-references of standard sizes to the host memory.

With this patch we attempt to provide unrestricted access to the RAM
device, allowing byte through qword access as well as unaligned
access.  The assumption here is that accesses initiated by the VM are
driven by a device specific driver, which knows the device
capabilities.  If unaligned accesses are not supported by the device,
we don't want them to work in a VM by performing multiple aligned
accesses to compose the unaligned access.  A down-side of this
philosophy is that the xp command from the monitor attempts to use
the largest available access weidth, unaware of the underlying
device.  Using memcpy had this same restriction, but at least now an
operator can dump individual registers, even if blocks of device
memory may result in access widths beyond the capabilities of a
given device (RTL NICs only support up to dword).

Reported-by: Thorsten Kohfeldt <thorsten.kohfeldt@gmx.de>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 include/exec/memory.h |    6 +++-
 memory.c              |   67 +++++++++++++++++++++++++++++++++++++++++++++++++
 trace-events          |    2 +
 3 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index a75b8c3..9728a2f 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1480,9 +1480,11 @@ void *qemu_map_ram_ptr(RAMBlock *ram_block, ram_addr_t addr);
 static inline bool memory_access_is_direct(MemoryRegion *mr, bool is_write)
 {
     if (is_write) {
-        return memory_region_is_ram(mr) && !mr->readonly;
+        return memory_region_is_ram(mr) &&
+               !mr->readonly && !memory_region_is_ram_device(mr);
     } else {
-        return memory_region_is_ram(mr) || memory_region_is_romd(mr);
+        return (memory_region_is_ram(mr) && !memory_region_is_ram_device(mr)) ||
+               memory_region_is_romd(mr);
     }
 }
 
diff --git a/memory.c b/memory.c
index 7ffcff1..33110e9 100644
--- a/memory.c
+++ b/memory.c
@@ -1128,6 +1128,71 @@ const MemoryRegionOps unassigned_mem_ops = {
     .endianness = DEVICE_NATIVE_ENDIAN,
 };
 
+static uint64_t memory_region_ram_device_read(void *opaque,
+                                              hwaddr addr, unsigned size)
+{
+    MemoryRegion *mr = opaque;
+    uint64_t data = (uint64_t)~0;
+
+    switch (size) {
+    case 1:
+        data = *(uint8_t *)(mr->ram_block->host + addr);
+        break;
+    case 2:
+        data = *(uint16_t *)(mr->ram_block->host + addr);
+        break;
+    case 4:
+        data = *(uint32_t *)(mr->ram_block->host + addr);
+        break;
+    case 8:
+        data = *(uint64_t *)(mr->ram_block->host + addr);
+        break;
+    }
+
+    trace_memory_region_ram_device_read(get_cpu_index(), mr, addr, data, size);
+
+    return data;
+}
+
+static void memory_region_ram_device_write(void *opaque, hwaddr addr,
+                                           uint64_t data, unsigned size)
+{
+    MemoryRegion *mr = opaque;
+
+    trace_memory_region_ram_device_write(get_cpu_index(), mr, addr, data, size);
+
+    switch (size) {
+    case 1:
+        *(uint8_t *)(mr->ram_block->host + addr) = (uint8_t)data;
+        break;
+    case 2:
+        *(uint16_t *)(mr->ram_block->host + addr) = (uint16_t)data;
+        break;
+    case 4:
+        *(uint32_t *)(mr->ram_block->host + addr) = (uint32_t)data;
+        break;
+    case 8:
+        *(uint64_t *)(mr->ram_block->host + addr) = data;
+        break;
+    }
+}
+
+static const MemoryRegionOps ram_device_mem_ops = {
+    .read = memory_region_ram_device_read,
+    .write = memory_region_ram_device_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+    .valid = {
+        .min_access_size = 1,
+        .max_access_size = 8,
+        .unaligned = true,
+    },
+    .impl = {
+        .min_access_size = 1,
+        .max_access_size = 8,
+        .unaligned = true,
+    },
+};
+
 bool memory_region_access_valid(MemoryRegion *mr,
                                 hwaddr addr,
                                 unsigned size,
@@ -1363,6 +1428,8 @@ void memory_region_init_ram_device_ptr(MemoryRegion *mr,
 {
     memory_region_init_ram_ptr(mr, owner, name, size, ptr);
     mr->ram_device = true;
+    mr->ops = &ram_device_mem_ops;
+    mr->opaque = mr;
 }
 
 void memory_region_init_alias(MemoryRegion *mr,
diff --git a/trace-events b/trace-events
index 8ecded5..f74e1d3 100644
--- a/trace-events
+++ b/trace-events
@@ -121,6 +121,8 @@ memory_region_subpage_read(int cpu_index, void *mr, uint64_t offset, uint64_t va
 memory_region_subpage_write(int cpu_index, void *mr, uint64_t offset, uint64_t value, unsigned size) "cpu %d mr %p offset %#"PRIx64" value %#"PRIx64" size %u"
 memory_region_tb_read(int cpu_index, uint64_t addr, uint64_t value, unsigned size) "cpu %d addr %#"PRIx64" value %#"PRIx64" size %u"
 memory_region_tb_write(int cpu_index, uint64_t addr, uint64_t value, unsigned size) "cpu %d addr %#"PRIx64" value %#"PRIx64" size %u"
+memory_region_ram_device_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr %#"PRIx64" value %#"PRIx64" size %u"
+memory_region_ram_device_write(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr %#"PRIx64" value %#"PRIx64" size %u"
 
 ### Guest events, keep at bottom
 

Re: [Qemu-devel] [PATCH v2 0/2] memory: Convert skip_dump to ram_device and avoid memcpy

[Paolo Bonzini]

On 25/10/2016 20:17, Alex Williamson wrote:
> v2: retain ram_device flag to avoid extra cache miss, per Paolo.
> 
> Paolo, posting for completeness, I can merge through my tree if you
> want to Ack.  Thanks,

Great, thanks.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

> Alex
> 
> ---
> 
> Alex Williamson (2):
>       memory: Replace skip_dump flag with "ram_device"
>       memory: Don't use memcpy for ram_device regions
> 
> 
>  hw/vfio/common.c      |    9 ++----
>  hw/vfio/spapr.c       |    2 +
>  include/exec/memory.h |   47 ++++++++++++++++++++---------
>  memory.c              |   80 +++++++++++++++++++++++++++++++++++++++++++++++--
>  memory_mapping.c      |    2 +
>  trace-events          |    2 +
>  6 files changed, 116 insertions(+), 26 deletions(-)
> 
> 

Re: [Qemu-devel] [PATCH v2 0/2] memory: Convert skip_dump to ram_device and avoid memcpy

[Thorsten Kohfeldt]

I tested these
https://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg05900.html
https://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg05901.html
https://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg05902.html

together with [Qemu-devel] [PULL 18/19] vfio/pci: Fix vfio_rtl8168_quirk_data_read add
https://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg03911.html

on top of qemu-stable-2.7.0

successfully on IPFire (Linux) and Windows 10 x64 with the Realtek driver.

I suggest all 3 commits (msg05901, msg05902, and msg03911) should become
serious candidates for qemu-2.7.1.

Regards,

Thorsten

Am 25.10.2016 um 20:17 schrieb Alex Williamson:
> v2: retain ram_device flag to avoid extra cache miss, per Paolo.
>
> Paolo, posting for completeness, I can merge through my tree if you
> want to Ack.  Thanks,
>
> Alex
>
> ---
>
> Alex Williamson (2):
>       memory: Replace skip_dump flag with "ram_device"
>       memory: Don't use memcpy for ram_device regions
>
>
>  hw/vfio/common.c      |    9 ++----
>  hw/vfio/spapr.c       |    2 +
>  include/exec/memory.h |   47 ++++++++++++++++++++---------
>  memory.c              |   80 +++++++++++++++++++++++++++++++++++++++++++++++--
>  memory_mapping.c      |    2 +
>  trace-events          |    2 +
>  6 files changed, 116 insertions(+), 26 deletions(-)
>