[PATCH v2 0/2] hw/arm/virt: Support for virtio-mem-pci

[PATCH v2 0/2] hw/arm/virt: Support for virtio-mem-pci

[Gavin Shan]

This series supports virtio-mem-pci device, by simply following the
implementation on x86. The exception is the block size is 512MB on
ARM64 instead of 128MB on x86, compatible with the memory section
size in linux guest.

The work was done by David Hildenbrand and then Jonathan Cameron. I'm
taking the patch and putting more efforts, which is all about testing
to me at current stage.

Testing
=======
The upstream linux kernel (v5.16.rc3) is used on host/guest during
the testing. The guest kernel includes changes to enable virtio-mem
driver, which is simply to enable CONFIG_VIRTIO_MEM on ARM64.

Mutiple combinations like page sizes on host/guest, memory backend
device etc are covered in the testing. Besides, migration is also
tested. The following command lines are used for VM or virtio-mem-pci
device hot-add. It's notable that virtio-mem-pci device hot-remove
isn't supported, similar to what we have on x86. 

  host.pgsize  guest.pgsize  backend    hot-add  hot-remove  migration
  ---------------------------------------------------------------------
   4KB         4KB           normal     ok       ok          ok
                             THP        ok       ok          ok
                             hugeTLB    ok       ok          ok
   4KB         64KB          normal     ok       ok          ok
                             THP        ok       ok          ok
                             hugeTLB    ok       ok          ok
  64KB         4KB           normal     ok       ok          ok
                             THP        ok       ok          ok
                             hugeTLB    ok       ok          ok
  64KB         64KB          normal     ok       ok          ok
                             THP        ok       ok          ok
                             hugeTLB    ok       ok          ok

The command lines are used for VM. When hugeTLBfs is used, all memory
backend objects are popuated on /dev/hugepages-2048kB or
/dev/hugepages-524288kB, depending on the host page sizes.

  /home/gavin/sandbox/qemu.main/build/qemu-system-aarch64                       \
  -accel kvm -machine virt,gic-version=host                                     \
  -cpu host -smp 4,sockets=2,cores=2,threads=1                                  \
  -m 1024M,slots=16,maxmem=64G                                                  \
  -object memory-backend-ram,id=mem0,size=512M                                  \
  -object memory-backend-ram,id=mem1,size=512M                                  \
  -numa node,nodeid=0,cpus=0-1,memdev=mem0                                      \
  -numa node,nodeid=1,cpus=2-3,memdev=mem1                                      \
     :
  -kernel /home/gavin/sandbox/linux.guest/arch/arm64/boot/Image                 \
  -initrd /home/gavin/sandbox/images/rootfs.cpio.xz                             \
  -append earlycon=pl011,mmio,0x9000000                                         \
  -device pcie-root-port,bus=pcie.0,chassis=1,id=pcie.1                         \
  -device pcie-root-port,bus=pcie.0,chassis=2,id=pcie.2                         \
  -device pcie-root-port,bus=pcie.0,chassis=3,id=pcie.3                         \
  -object memory-backend-ram,id=vmem0,size=512M                                 \
  -device virtio-mem-pci,id=vm0,bus=pcie.1,memdev=vmem0,node=0,requested-size=0 \
  -object memory-backend-ram,id=vmem1,size=512M                                 \
  -device virtio-mem-pci,id=vm1,bus=pcie.2,memdev=vmem1,node=1,requested-size=0 

Command lines used for memory hot-add and hot-remove:

  (qemu) qom-set vm1 requested-size 512M
  (qemu) qom-set vm1 requested-size 0
  (qemu) qom-set vm1 requested-size 512M

Command lines used for virtio-mem-pci device hot-add:

  (qemu) object_add memory-backend-ram,id=hp-mem1,size=512M
  (qemu) device_add virtio-mem-pci,id=hp-vm1,bus=pcie.3,memdev=hp-mem1,node=1
  (qemu) qom-set hp-vm1 requested-size 512M
  (qemu) qom-set hp-vm1 requested-size 0
  (qemu) qom-set hp-vm1 requested-size 512M

Changelog
=========
v2:
  * Include David/Jonathan as co-developers in the commit log           (David)
  * Decrease VIRTIO_MEM_USABLE_EXTENT to 512MB on ARM64 in PATCH[1/2]   (David)
  * PATCH[2/2] is added to correct the THP sizes on ARM64               (David)

Gavin Shan (2):
  hw/arm/virt: Support for virtio-mem-pci
  virtio-mem: Correct default THP size for ARM64

 hw/arm/Kconfig         |  1 +
 hw/arm/virt.c          | 68 +++++++++++++++++++++++++++++++++++++++++-
 hw/virtio/virtio-mem.c | 36 ++++++++++++++--------
 3 files changed, 91 insertions(+), 14 deletions(-)

-- 
2.23.0

[PATCH v2 1/2] hw/arm/virt: Support for virtio-mem-pci

[Gavin Shan]

This supports virtio-mem-pci device on "virt" platform, by simply
following the implementation on x86.

   * This implements the hotplug handlers to support virtio-mem-pci
     device hot-add, while the hot-remove isn't supported as we have
     on x86.

   * The block size is 512MB on ARM64 instead of 128MB on x86.

   * It has been passing the tests with various combinations like 64KB
     and 4KB page sizes on host and guest, different memory device
     backends like normal, transparent huge page and HugeTLB, plus
     migration.

Co-developed-by: David Hildenbrand <david@redhat.com>
Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 hw/arm/Kconfig         |  1 +
 hw/arm/virt.c          | 68 +++++++++++++++++++++++++++++++++++++++++-
 hw/virtio/virtio-mem.c |  4 ++-
 3 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/hw/arm/Kconfig b/hw/arm/Kconfig
index 2d37d29f02..15aff8efb8 100644
--- a/hw/arm/Kconfig
+++ b/hw/arm/Kconfig
@@ -27,6 +27,7 @@ config ARM_VIRT
     select DIMM
     select ACPI_HW_REDUCED
     select ACPI_APEI
+    select VIRTIO_MEM_SUPPORTED
 
 config CHEETAH
     bool
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 369552ad45..f4599a5ef0 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -71,9 +71,11 @@
 #include "hw/arm/smmuv3.h"
 #include "hw/acpi/acpi.h"
 #include "target/arm/internals.h"
+#include "hw/mem/memory-device.h"
 #include "hw/mem/pc-dimm.h"
 #include "hw/mem/nvdimm.h"
 #include "hw/acpi/generic_event_device.h"
+#include "hw/virtio/virtio-mem-pci.h"
 #include "hw/virtio/virtio-iommu.h"
 #include "hw/char/pl011.h"
 #include "qemu/guest-random.h"
@@ -2480,6 +2482,63 @@ static void virt_memory_plug(HotplugHandler *hotplug_dev,
                          dev, &error_abort);
 }
 
+static void virt_virtio_md_pci_pre_plug(HotplugHandler *hotplug_dev,
+                                        DeviceState *dev, Error **errp)
+{
+    HotplugHandler *hotplug_dev2 = qdev_get_bus_hotplug_handler(dev);
+    Error *local_err = NULL;
+
+    if (!hotplug_dev2 && dev->hotplugged) {
+        /*
+         * Without a bus hotplug handler, we cannot control the plug/unplug
+         * order. We should never reach this point when hotplugging on x86,
+         * however, better add a safety net.
+         */
+        error_setg(errp, "hotplug of virtio based memory devices not supported"
+                   " on this bus.");
+        return;
+    }
+    /*
+     * First, see if we can plug this memory device at all. If that
+     * succeeds, branch of to the actual hotplug handler.
+     */
+    memory_device_pre_plug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev), NULL,
+                           &local_err);
+    if (!local_err && hotplug_dev2) {
+        hotplug_handler_pre_plug(hotplug_dev2, dev, &local_err);
+    }
+    error_propagate(errp, local_err);
+}
+
+static void virt_virtio_md_pci_plug(HotplugHandler *hotplug_dev,
+                                    DeviceState *dev, Error **errp)
+{
+    HotplugHandler *hotplug_dev2 = qdev_get_bus_hotplug_handler(dev);
+    Error *local_err = NULL;
+
+    /*
+     * Plug the memory device first and then branch off to the actual
+     * hotplug handler. If that one fails, we can easily undo the memory
+     * device bits.
+     */
+    memory_device_plug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev));
+    if (hotplug_dev2) {
+        hotplug_handler_plug(hotplug_dev2, dev, &local_err);
+        if (local_err) {
+            memory_device_unplug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev));
+        }
+    }
+    error_propagate(errp, local_err);
+}
+
+static void virt_virtio_md_pci_unplug_request(HotplugHandler *hotplug_dev,
+                                              DeviceState *dev, Error **errp)
+{
+    /* We don't support hot unplug of virtio based memory devices */
+    error_setg(errp, "virtio based memory devices cannot be unplugged.");
+}
+
+
 static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
                                             DeviceState *dev, Error **errp)
 {
@@ -2513,6 +2572,8 @@ static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
         qdev_prop_set_uint32(dev, "len-reserved-regions", 1);
         qdev_prop_set_string(dev, "reserved-regions[0]", resv_prop_str);
         g_free(resv_prop_str);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
+        virt_virtio_md_pci_pre_plug(hotplug_dev, dev, errp);
     }
 }
 
@@ -2538,6 +2599,8 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
         vms->iommu = VIRT_IOMMU_VIRTIO;
         vms->virtio_iommu_bdf = pci_get_bdf(pdev);
         create_virtio_iommu_dt_bindings(vms);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
+        virt_virtio_md_pci_plug(hotplug_dev, dev, errp);
     }
 }
 
@@ -2588,6 +2651,8 @@ static void virt_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
 {
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
         virt_dimm_unplug_request(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
+        virt_virtio_md_pci_unplug_request(hotplug_dev, dev, errp);
     } else {
         error_setg(errp, "device unplug request for unsupported device"
                    " type: %s", object_get_typename(OBJECT(dev)));
@@ -2611,7 +2676,8 @@ static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine,
     MachineClass *mc = MACHINE_GET_CLASS(machine);
 
     if (device_is_dynamic_sysbus(mc, dev) ||
-       (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM))) {
+        object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) ||
+        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
         return HOTPLUG_HANDLER(machine);
     }
     if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index d5a578142b..ac7a40f514 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -117,7 +117,7 @@ static uint64_t virtio_mem_default_block_size(RAMBlock *rb)
  * The memory block size corresponds mostly to the section size.
  *
  * This allows e.g., to add 20MB with a section size of 128MB on x86_64, and
- * a section size of 1GB on arm64 (as long as the start address is properly
+ * a section size of 512MB on arm64 (as long as the start address is properly
  * aligned, similar to ordinary DIMMs).
  *
  * We can change this at any time and maybe even make it configurable if
@@ -126,6 +126,8 @@ static uint64_t virtio_mem_default_block_size(RAMBlock *rb)
  */
 #if defined(TARGET_X86_64) || defined(TARGET_I386)
 #define VIRTIO_MEM_USABLE_EXTENT (2 * (128 * MiB))
+#elif defined(TARGET_ARM)
+#define VIRTIO_MEM_USABLE_EXTENT (2 * (512 * MiB))
 #else
 #error VIRTIO_MEM_USABLE_EXTENT not defined
 #endif
-- 
2.23.0

[PATCH v2 2/2] virtio-mem: Correct default THP size for ARM64

[Gavin Shan]

The default block size is same as to the THP size, which is either
retrieved from "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
or hardcoded to 2MB. There are flaws in both mechanisms and this
intends to fix them up.

  * When "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size" is
    used to getting the THP size, 32MB and 512MB are valid values
    when we have 16KB and 64KB page size on ARM64.

  * When the hardcoded THP size is used, 2MB, 32MB and 512MB are
    valid values when we have 4KB, 16KB and 64KB page sizes on
    ARM64.

Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 hw/virtio/virtio-mem.c | 32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index ac7a40f514..8f3c95300f 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -38,14 +38,25 @@
  */
 #define VIRTIO_MEM_MIN_BLOCK_SIZE ((uint32_t)(1 * MiB))
 
-#if defined(__x86_64__) || defined(__arm__) || defined(__aarch64__) || \
-    defined(__powerpc64__)
-#define VIRTIO_MEM_DEFAULT_THP_SIZE ((uint32_t)(2 * MiB))
-#else
-        /* fallback to 1 MiB (e.g., the THP size on s390x) */
-#define VIRTIO_MEM_DEFAULT_THP_SIZE VIRTIO_MEM_MIN_BLOCK_SIZE
+static uint32_t virtio_mem_default_thp_size(void)
+{
+    uint32_t default_thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
+
+#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__)
+    default_thp_size = (uint32_t)(2 * MiB);
+#elif defined(__aarch64__)
+    if (qemu_real_host_page_size == (4 * KiB)) {
+        default_thp_size = (uint32_t)(2 * MiB);
+    } else if (qemu_real_host_page_size == (16 * KiB)) {
+        default_thp_size = (uint32_t)(32 * MiB);
+    } else if (qemu_real_host_page_size == (64 * KiB)) {
+        default_thp_size = (uint32_t)(512 * MiB);
+    }
 #endif
 
+    return default_thp_size;
+}
+
 /*
  * We want to have a reasonable default block size such that
  * 1. We avoid splitting THPs when unplugging memory, which degrades
@@ -78,11 +89,8 @@ static uint32_t virtio_mem_thp_size(void)
     if (g_file_get_contents(HPAGE_PMD_SIZE_PATH, &content, NULL, NULL) &&
         !qemu_strtou64(content, &endptr, 0, &tmp) &&
         (!endptr || *endptr == '\n')) {
-        /*
-         * Sanity-check the value, if it's too big (e.g., aarch64 with 64k base
-         * pages) or weird, fallback to something smaller.
-         */
-        if (!tmp || !is_power_of_2(tmp) || tmp > 16 * MiB) {
+        /* Sanity-check the value and fallback to something reasonable. */
+        if (!tmp || !is_power_of_2(tmp)) {
             warn_report("Read unsupported THP size: %" PRIx64, tmp);
         } else {
             thp_size = tmp;
@@ -90,7 +98,7 @@ static uint32_t virtio_mem_thp_size(void)
     }
 
     if (!thp_size) {
-        thp_size = VIRTIO_MEM_DEFAULT_THP_SIZE;
+        thp_size = virtio_mem_default_thp_size();
         warn_report("Could not detect THP size, falling back to %" PRIx64
                     "  MiB.", thp_size / MiB);
     }
-- 
2.23.0

Re: [PATCH v2 0/2] hw/arm/virt: Support for virtio-mem-pci

[Jonathan Cameron via]

On Fri,  3 Dec 2021 11:35:20 +0800
Gavin Shan <gshan@redhat.com> wrote:

> This series supports virtio-mem-pci device, by simply following the
> implementation on x86. The exception is the block size is 512MB on
> ARM64 instead of 128MB on x86, compatible with the memory section
> size in linux guest.
> 
> The work was done by David Hildenbrand and then Jonathan Cameron. I'm
> taking the patch and putting more efforts, which is all about testing
> to me at current stage.

Hi Gavin,

Thanks for taking this forwards.  What you have here looks good to me, but
I've not looked at this for a while, so I'll go with whatever David and
others say :)

Jonathan

> 
> Testing
> =======
> The upstream linux kernel (v5.16.rc3) is used on host/guest during
> the testing. The guest kernel includes changes to enable virtio-mem
> driver, which is simply to enable CONFIG_VIRTIO_MEM on ARM64.
> 
> Mutiple combinations like page sizes on host/guest, memory backend
> device etc are covered in the testing. Besides, migration is also
> tested. The following command lines are used for VM or virtio-mem-pci
> device hot-add. It's notable that virtio-mem-pci device hot-remove
> isn't supported, similar to what we have on x86. 
> 
>   host.pgsize  guest.pgsize  backend    hot-add  hot-remove  migration
>   ---------------------------------------------------------------------
>    4KB         4KB           normal     ok       ok          ok
>                              THP        ok       ok          ok
>                              hugeTLB    ok       ok          ok
>    4KB         64KB          normal     ok       ok          ok
>                              THP        ok       ok          ok
>                              hugeTLB    ok       ok          ok
>   64KB         4KB           normal     ok       ok          ok
>                              THP        ok       ok          ok
>                              hugeTLB    ok       ok          ok
>   64KB         64KB          normal     ok       ok          ok
>                              THP        ok       ok          ok
>                              hugeTLB    ok       ok          ok
> 
> The command lines are used for VM. When hugeTLBfs is used, all memory
> backend objects are popuated on /dev/hugepages-2048kB or
> /dev/hugepages-524288kB, depending on the host page sizes.
> 
>   /home/gavin/sandbox/qemu.main/build/qemu-system-aarch64                       \
>   -accel kvm -machine virt,gic-version=host                                     \
>   -cpu host -smp 4,sockets=2,cores=2,threads=1                                  \
>   -m 1024M,slots=16,maxmem=64G                                                  \
>   -object memory-backend-ram,id=mem0,size=512M                                  \
>   -object memory-backend-ram,id=mem1,size=512M                                  \
>   -numa node,nodeid=0,cpus=0-1,memdev=mem0                                      \
>   -numa node,nodeid=1,cpus=2-3,memdev=mem1                                      \
>      :
>   -kernel /home/gavin/sandbox/linux.guest/arch/arm64/boot/Image                 \
>   -initrd /home/gavin/sandbox/images/rootfs.cpio.xz                             \
>   -append earlycon=pl011,mmio,0x9000000                                         \
>   -device pcie-root-port,bus=pcie.0,chassis=1,id=pcie.1                         \
>   -device pcie-root-port,bus=pcie.0,chassis=2,id=pcie.2                         \
>   -device pcie-root-port,bus=pcie.0,chassis=3,id=pcie.3                         \
>   -object memory-backend-ram,id=vmem0,size=512M                                 \
>   -device virtio-mem-pci,id=vm0,bus=pcie.1,memdev=vmem0,node=0,requested-size=0 \
>   -object memory-backend-ram,id=vmem1,size=512M                                 \
>   -device virtio-mem-pci,id=vm1,bus=pcie.2,memdev=vmem1,node=1,requested-size=0 
> 
> Command lines used for memory hot-add and hot-remove:
> 
>   (qemu) qom-set vm1 requested-size 512M
>   (qemu) qom-set vm1 requested-size 0
>   (qemu) qom-set vm1 requested-size 512M
> 
> Command lines used for virtio-mem-pci device hot-add:
> 
>   (qemu) object_add memory-backend-ram,id=hp-mem1,size=512M
>   (qemu) device_add virtio-mem-pci,id=hp-vm1,bus=pcie.3,memdev=hp-mem1,node=1
>   (qemu) qom-set hp-vm1 requested-size 512M
>   (qemu) qom-set hp-vm1 requested-size 0
>   (qemu) qom-set hp-vm1 requested-size 512M
> 
> Changelog
> =========
> v2:
>   * Include David/Jonathan as co-developers in the commit log           (David)
>   * Decrease VIRTIO_MEM_USABLE_EXTENT to 512MB on ARM64 in PATCH[1/2]   (David)
>   * PATCH[2/2] is added to correct the THP sizes on ARM64               (David)
> 
> Gavin Shan (2):
>   hw/arm/virt: Support for virtio-mem-pci
>   virtio-mem: Correct default THP size for ARM64
> 
>  hw/arm/Kconfig         |  1 +
>  hw/arm/virt.c          | 68 +++++++++++++++++++++++++++++++++++++++++-
>  hw/virtio/virtio-mem.c | 36 ++++++++++++++--------
>  3 files changed, 91 insertions(+), 14 deletions(-)
> 

Re: [PATCH v2 2/2] virtio-mem: Correct default THP size for ARM64

[David Hildenbrand]

On 03.12.21 04:35, Gavin Shan wrote:
> The default block size is same as to the THP size, which is either
> retrieved from "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
> or hardcoded to 2MB. There are flaws in both mechanisms and this
> intends to fix them up.
> 
>   * When "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size" is
>     used to getting the THP size, 32MB and 512MB are valid values
>     when we have 16KB and 64KB page size on ARM64.

Ah, right, there is 16KB as well :)

> 
>   * When the hardcoded THP size is used, 2MB, 32MB and 512MB are
>     valid values when we have 4KB, 16KB and 64KB page sizes on
>     ARM64.
> 
> Co-developed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  hw/virtio/virtio-mem.c | 32 ++++++++++++++++++++------------
>  1 file changed, 20 insertions(+), 12 deletions(-)
> 
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index ac7a40f514..8f3c95300f 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -38,14 +38,25 @@
>   */
>  #define VIRTIO_MEM_MIN_BLOCK_SIZE ((uint32_t)(1 * MiB))
>  
> -#if defined(__x86_64__) || defined(__arm__) || defined(__aarch64__) || \
> -    defined(__powerpc64__)
> -#define VIRTIO_MEM_DEFAULT_THP_SIZE ((uint32_t)(2 * MiB))
> -#else
> -        /* fallback to 1 MiB (e.g., the THP size on s390x) */
> -#define VIRTIO_MEM_DEFAULT_THP_SIZE VIRTIO_MEM_MIN_BLOCK_SIZE
> +static uint32_t virtio_mem_default_thp_size(void)
> +{
> +    uint32_t default_thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
> +
> +#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__)
> +    default_thp_size = (uint32_t)(2 * MiB);
> +#elif defined(__aarch64__)
> +    if (qemu_real_host_page_size == (4 * KiB)) {

you can drop the superfluous (), also in the cases below.

> +        default_thp_size = (uint32_t)(2 * MiB);

The explicit cast shouldn't be required.

> +    } else if (qemu_real_host_page_size == (16 * KiB)) {
> +        default_thp_size = (uint32_t)(32 * MiB);
> +    } else if (qemu_real_host_page_size == (64 * KiB)) {
> +        default_thp_size = (uint32_t)(512 * MiB);
> +    }
>  #endif
>  
> +    return default_thp_size;
> +}
> +
>  /*
>   * We want to have a reasonable default block size such that
>   * 1. We avoid splitting THPs when unplugging memory, which degrades
> @@ -78,11 +89,8 @@ static uint32_t virtio_mem_thp_size(void)
>      if (g_file_get_contents(HPAGE_PMD_SIZE_PATH, &content, NULL, NULL) &&
>          !qemu_strtou64(content, &endptr, 0, &tmp) &&
>          (!endptr || *endptr == '\n')) {
> -        /*
> -         * Sanity-check the value, if it's too big (e.g., aarch64 with 64k base
> -         * pages) or weird, fallback to something smaller.
> -         */
> -        if (!tmp || !is_power_of_2(tmp) || tmp > 16 * MiB) {
> +        /* Sanity-check the value and fallback to something reasonable. */
> +        if (!tmp || !is_power_of_2(tmp)) {
>              warn_report("Read unsupported THP size: %" PRIx64, tmp);
>          } else {
>              thp_size = tmp;
> @@ -90,7 +98,7 @@ static uint32_t virtio_mem_thp_size(void)
>      }
>  
>      if (!thp_size) {
> -        thp_size = VIRTIO_MEM_DEFAULT_THP_SIZE;
> +        thp_size = virtio_mem_default_thp_size();
>          warn_report("Could not detect THP size, falling back to %" PRIx64
>                      "  MiB.", thp_size / MiB);
>      }
> 

Apart from that,

Reviewed-by: David Hildenbrand <david@redhat.com>


Thanks!

-- 
Thanks,

David / dhildenb

Re: [PATCH v2 1/2] hw/arm/virt: Support for virtio-mem-pci

[David Hildenbrand]

On 03.12.21 04:35, Gavin Shan wrote:
> This supports virtio-mem-pci device on "virt" platform, by simply
> following the implementation on x86.
> 
>    * This implements the hotplug handlers to support virtio-mem-pci
>      device hot-add, while the hot-remove isn't supported as we have
>      on x86.
> 
>    * The block size is 512MB on ARM64 instead of 128MB on x86.
> 
>    * It has been passing the tests with various combinations like 64KB
>      and 4KB page sizes on host and guest, different memory device
>      backends like normal, transparent huge page and HugeTLB, plus
>      migration.
> 

I would turn this patch into 2/2, reshuffling both patches.

> Co-developed-by: David Hildenbrand <david@redhat.com>
> Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Gavin Shan <gshan@redhat.com>

Reviewed-by: David Hildenbrand <david@redhat.com>

Thanks Gavin!

-- 
Thanks,

David / dhildenb

Re: [PATCH v2 0/2] hw/arm/virt: Support for virtio-mem-pci

[Gavin Shan]

Hi Jonathan,

On 12/4/21 1:10 AM, Jonathan Cameron wrote:
> On Fri,  3 Dec 2021 11:35:20 +0800
> Gavin Shan <gshan@redhat.com> wrote:
> 
>> This series supports virtio-mem-pci device, by simply following the
>> implementation on x86. The exception is the block size is 512MB on
>> ARM64 instead of 128MB on x86, compatible with the memory section
>> size in linux guest.
>>
>> The work was done by David Hildenbrand and then Jonathan Cameron. I'm
>> taking the patch and putting more efforts, which is all about testing
>> to me at current stage.
> 
> Thanks for taking this forwards.  What you have here looks good to me, but
> I've not looked at this for a while, so I'll go with whatever David and
> others say :)
> 

[...]

I would translate this as your reviewed-by tag, which will be added to v3.
However, it shouldn't stop you from further reviewing :)

Thanks,
Gavin

Re: [PATCH v2 1/2] hw/arm/virt: Support for virtio-mem-pci

[Gavin Shan]

On 12/4/21 5:18 AM, David Hildenbrand wrote:
> On 03.12.21 04:35, Gavin Shan wrote:
>> This supports virtio-mem-pci device on "virt" platform, by simply
>> following the implementation on x86.
>>
>>     * This implements the hotplug handlers to support virtio-mem-pci
>>       device hot-add, while the hot-remove isn't supported as we have
>>       on x86.
>>
>>     * The block size is 512MB on ARM64 instead of 128MB on x86.
>>
>>     * It has been passing the tests with various combinations like 64KB
>>       and 4KB page sizes on host and guest, different memory device
>>       backends like normal, transparent huge page and HugeTLB, plus
>>       migration.
>>
> 
> I would turn this patch into 2/2, reshuffling both patches.
> 
>> Co-developed-by: David Hildenbrand <david@redhat.com>
>> Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> 
> Thanks Gavin!
> 

Yup, I thought of it. The fixed issue doesn't exist if virtio-mem
isn't enabled on ARM64 with PATCH[1/2]. That's why I have this
patch as PATCH[2/2]. However, It's also sensible to me to reshuffle
the patches: to eliminate potential issues before enabling virtio-mem
on ARM64. v3 will have the changes :)

Thanks,
Gavin

Re: [PATCH v2 2/2] virtio-mem: Correct default THP size for ARM64

[Gavin Shan]

On 12/4/21 5:16 AM, David Hildenbrand wrote:
> On 03.12.21 04:35, Gavin Shan wrote:
>> The default block size is same as to the THP size, which is either
>> retrieved from "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
>> or hardcoded to 2MB. There are flaws in both mechanisms and this
>> intends to fix them up.
>>
>>    * When "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size" is
>>      used to getting the THP size, 32MB and 512MB are valid values
>>      when we have 16KB and 64KB page size on ARM64.
> 
> Ah, right, there is 16KB as well :)
> 

Yep, even though it's rarely used :)

>>
>>    * When the hardcoded THP size is used, 2MB, 32MB and 512MB are
>>      valid values when we have 4KB, 16KB and 64KB page sizes on
>>      ARM64.
>>
>> Co-developed-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   hw/virtio/virtio-mem.c | 32 ++++++++++++++++++++------------
>>   1 file changed, 20 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
>> index ac7a40f514..8f3c95300f 100644
>> --- a/hw/virtio/virtio-mem.c
>> +++ b/hw/virtio/virtio-mem.c
>> @@ -38,14 +38,25 @@
>>    */
>>   #define VIRTIO_MEM_MIN_BLOCK_SIZE ((uint32_t)(1 * MiB))
>>   
>> -#if defined(__x86_64__) || defined(__arm__) || defined(__aarch64__) || \
>> -    defined(__powerpc64__)
>> -#define VIRTIO_MEM_DEFAULT_THP_SIZE ((uint32_t)(2 * MiB))
>> -#else
>> -        /* fallback to 1 MiB (e.g., the THP size on s390x) */
>> -#define VIRTIO_MEM_DEFAULT_THP_SIZE VIRTIO_MEM_MIN_BLOCK_SIZE
>> +static uint32_t virtio_mem_default_thp_size(void)
>> +{
>> +    uint32_t default_thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
>> +
>> +#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__)
>> +    default_thp_size = (uint32_t)(2 * MiB);
>> +#elif defined(__aarch64__)
>> +    if (qemu_real_host_page_size == (4 * KiB)) {
> 
> you can drop the superfluous (), also in the cases below.
> 

It will be included in v3.

>> +        default_thp_size = (uint32_t)(2 * MiB);
> 
> The explicit cast shouldn't be required.
> 

It's not required, but inherited from the definition
of VIRTIO_MEM_MIN_BLOCK_SIZE. However, it's safe to
drop the cast and it will be included in v3.

>> +    } else if (qemu_real_host_page_size == (16 * KiB)) {
>> +        default_thp_size = (uint32_t)(32 * MiB);
>> +    } else if (qemu_real_host_page_size == (64 * KiB)) {
>> +        default_thp_size = (uint32_t)(512 * MiB);
>> +    }
>>   #endif
>>   
>> +    return default_thp_size;
>> +}
>> +
>>   /*
>>    * We want to have a reasonable default block size such that
>>    * 1. We avoid splitting THPs when unplugging memory, which degrades
>> @@ -78,11 +89,8 @@ static uint32_t virtio_mem_thp_size(void)
>>       if (g_file_get_contents(HPAGE_PMD_SIZE_PATH, &content, NULL, NULL) &&
>>           !qemu_strtou64(content, &endptr, 0, &tmp) &&
>>           (!endptr || *endptr == '\n')) {
>> -        /*
>> -         * Sanity-check the value, if it's too big (e.g., aarch64 with 64k base
>> -         * pages) or weird, fallback to something smaller.
>> -         */
>> -        if (!tmp || !is_power_of_2(tmp) || tmp > 16 * MiB) {
>> +        /* Sanity-check the value and fallback to something reasonable. */
>> +        if (!tmp || !is_power_of_2(tmp)) {
>>               warn_report("Read unsupported THP size: %" PRIx64, tmp);
>>           } else {
>>               thp_size = tmp;
>> @@ -90,7 +98,7 @@ static uint32_t virtio_mem_thp_size(void)
>>       }
>>   
>>       if (!thp_size) {
>> -        thp_size = VIRTIO_MEM_DEFAULT_THP_SIZE;
>> +        thp_size = virtio_mem_default_thp_size();
>>           warn_report("Could not detect THP size, falling back to %" PRIx64
>>                       "  MiB.", thp_size / MiB);
>>       }
>>
> 
> Apart from that,
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> 

Thanks for your review, David!

Thanks,
Gavin