[PATCH v5 0/6] hw/arm/virt: Improve address assignment for high memory regions

[PATCH v5 0/6] hw/arm/virt: Improve address assignment for high memory regions

[Gavin Shan]

There are three high memory regions, which are VIRT_HIGH_REDIST2,
VIRT_HIGH_PCIE_ECAM and VIRT_HIGH_PCIE_MMIO. Their base addresses
are floating on highest RAM address. However, they can be disabled
in several cases.

(1) One specific high memory region is disabled by developer by
    toggling vms->highmem_{redists, ecam, mmio}.

(2) VIRT_HIGH_PCIE_ECAM region is disabled on machine, which is
    'virt-2.12' or ealier than it.

(3) VIRT_HIGH_PCIE_ECAM region is disabled when firmware is loaded
    on 32-bits system.

(4) One specific high memory region is disabled when it breaks the
    PA space limit.

The current implementation of virt_set_memmap() isn't comprehensive
because the space for one specific high memory region is always
reserved from the PA space for case (1), (2) and (3). In the code,
'base' and 'vms->highest_gpa' are always increased for those three
cases. It's unnecessary since the assigned space of the disabled
high memory region won't be used afterwards.

The series intends to improve the address assignment for these
high memory regions.

PATCH[1-4] preparatory work for the improvment
PATCH[5]   improve high memory region address assignment
PATCH[6]   adds 'compact-highmem' to enable or disable the optimization

v4: https://lists.nongnu.org/archive/html/qemu-arm/2022-10/msg00067.html
v3: https://lists.nongnu.org/archive/html/qemu-arm/2022-09/msg00258.html
v2: https://lore.kernel.org/all/20220815062958.100366-1-gshan@redhat.com/T/
v1: https://lists.nongnu.org/archive/html/qemu-arm/2022-08/msg00013.html

Changelog
==========
v5:
  * Pick review-by and tested-by                               (Connie/Zhenyu)
  * Add extra check in PATCH[v5 4/6]                           (Connie)
  * Improve comments about compatibility for disabled regions
    in PATCH[v5 5/6]                                           (Connie)
v4:
  * Add virt_get_high_memmap_enabled() helper                  (Eric)
  * Move 'vms->highmem_compact' and related logic from
    PATCH[v4 6/6] to PATCH[v4 5/6] to avoid git-bisect
    breakage                                                   (Eric)
  * Document the legacy and optimized high memory region
    layout in commit log and source code                       (Eric)
v3:
  * Reorder the patches                                        (Gavin)
  * Add 'highmem-compact' property for backwards compatibility (Eric)
v2:
  * Split the patches for easier review                        (Gavin)
  * Improved changelog                                         (Marc)
  * Use 'bool fits' in virt_set_high_memmap()                  (Eric)

Gavin Shan (6):
  hw/arm/virt: Introduce virt_set_high_memmap() helper
  hw/arm/virt: Rename variable size to region_size in
    virt_set_high_memmap()
  hw/arm/virt: Introduce variable region_base in virt_set_high_memmap()
  hw/arm/virt: Introduce virt_get_high_memmap_enabled() helper
  hw/arm/virt: Improve high memory region address assignment
  hw/arm/virt: Add 'compact-highmem' property

 docs/system/arm/virt.rst |   4 ++
 hw/arm/virt.c            | 135 +++++++++++++++++++++++++++++----------
 include/hw/arm/virt.h    |   2 +
 3 files changed, 108 insertions(+), 33 deletions(-)

-- 
2.23.0

[PATCH v5 1/6] hw/arm/virt: Introduce virt_set_high_memmap() helper

[Gavin Shan]

This introduces virt_set_high_memmap() helper. The logic of high
memory region address assignment is moved to the helper. The intention
is to make the subsequent optimization for high memory region address
assignment easier.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
---
 hw/arm/virt.c | 74 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 41 insertions(+), 33 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index cda9defe8f..7572c44bda 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1689,6 +1689,46 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
     return arm_cpu_mp_affinity(idx, clustersz);
 }
 
+static void virt_set_high_memmap(VirtMachineState *vms,
+                                 hwaddr base, int pa_bits)
+{
+    int i;
+
+    for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
+        hwaddr size = extended_memmap[i].size;
+        bool fits;
+
+        base = ROUND_UP(base, size);
+        vms->memmap[i].base = base;
+        vms->memmap[i].size = size;
+
+        /*
+         * Check each device to see if they fit in the PA space,
+         * moving highest_gpa as we go.
+         *
+         * For each device that doesn't fit, disable it.
+         */
+        fits = (base + size) <= BIT_ULL(pa_bits);
+        if (fits) {
+            vms->highest_gpa = base + size - 1;
+        }
+
+        switch (i) {
+        case VIRT_HIGH_GIC_REDIST2:
+            vms->highmem_redists &= fits;
+            break;
+        case VIRT_HIGH_PCIE_ECAM:
+            vms->highmem_ecam &= fits;
+            break;
+        case VIRT_HIGH_PCIE_MMIO:
+            vms->highmem_mmio &= fits;
+            break;
+        }
+
+        base += size;
+    }
+}
+
 static void virt_set_memmap(VirtMachineState *vms, int pa_bits)
 {
     MachineState *ms = MACHINE(vms);
@@ -1744,39 +1784,7 @@ static void virt_set_memmap(VirtMachineState *vms, int pa_bits)
     /* We know for sure that at least the memory fits in the PA space */
     vms->highest_gpa = memtop - 1;
 
-    for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
-        hwaddr size = extended_memmap[i].size;
-        bool fits;
-
-        base = ROUND_UP(base, size);
-        vms->memmap[i].base = base;
-        vms->memmap[i].size = size;
-
-        /*
-         * Check each device to see if they fit in the PA space,
-         * moving highest_gpa as we go.
-         *
-         * For each device that doesn't fit, disable it.
-         */
-        fits = (base + size) <= BIT_ULL(pa_bits);
-        if (fits) {
-            vms->highest_gpa = base + size - 1;
-        }
-
-        switch (i) {
-        case VIRT_HIGH_GIC_REDIST2:
-            vms->highmem_redists &= fits;
-            break;
-        case VIRT_HIGH_PCIE_ECAM:
-            vms->highmem_ecam &= fits;
-            break;
-        case VIRT_HIGH_PCIE_MMIO:
-            vms->highmem_mmio &= fits;
-            break;
-        }
-
-        base += size;
-    }
+    virt_set_high_memmap(vms, base, pa_bits);
 
     if (device_memory_size > 0) {
         ms->device_memory = g_malloc0(sizeof(*ms->device_memory));
-- 
2.23.0

[PATCH v5 2/6] hw/arm/virt: Rename variable size to region_size in virt_set_high_memmap()

[Gavin Shan]

This renames variable 'size' to 'region_size' in virt_set_high_memmap().
Its counterpart ('region_base') will be introduced in next patch.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
---
 hw/arm/virt.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 7572c44bda..e2ae88cf8b 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1692,15 +1692,16 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
 static void virt_set_high_memmap(VirtMachineState *vms,
                                  hwaddr base, int pa_bits)
 {
+    hwaddr region_size;
+    bool fits;
     int i;
 
     for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
-        hwaddr size = extended_memmap[i].size;
-        bool fits;
+        region_size = extended_memmap[i].size;
 
-        base = ROUND_UP(base, size);
+        base = ROUND_UP(base, region_size);
         vms->memmap[i].base = base;
-        vms->memmap[i].size = size;
+        vms->memmap[i].size = region_size;
 
         /*
          * Check each device to see if they fit in the PA space,
@@ -1708,9 +1709,9 @@ static void virt_set_high_memmap(VirtMachineState *vms,
          *
          * For each device that doesn't fit, disable it.
          */
-        fits = (base + size) <= BIT_ULL(pa_bits);
+        fits = (base + region_size) <= BIT_ULL(pa_bits);
         if (fits) {
-            vms->highest_gpa = base + size - 1;
+            vms->highest_gpa = base + region_size - 1;
         }
 
         switch (i) {
@@ -1725,7 +1726,7 @@ static void virt_set_high_memmap(VirtMachineState *vms,
             break;
         }
 
-        base += size;
+        base += region_size;
     }
 }
 
-- 
2.23.0

[PATCH v5 3/6] hw/arm/virt: Introduce variable region_base in virt_set_high_memmap()

[Gavin Shan]

This introduces variable 'region_base' for the base address of the
specific high memory region. It's the preparatory work to optimize
high memory region address assignment.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
---
 hw/arm/virt.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index e2ae88cf8b..0bf3cb7057 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1692,15 +1692,15 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
 static void virt_set_high_memmap(VirtMachineState *vms,
                                  hwaddr base, int pa_bits)
 {
-    hwaddr region_size;
+    hwaddr region_base, region_size;
     bool fits;
     int i;
 
     for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
+        region_base = ROUND_UP(base, extended_memmap[i].size);
         region_size = extended_memmap[i].size;
 
-        base = ROUND_UP(base, region_size);
-        vms->memmap[i].base = base;
+        vms->memmap[i].base = region_base;
         vms->memmap[i].size = region_size;
 
         /*
@@ -1709,9 +1709,9 @@ static void virt_set_high_memmap(VirtMachineState *vms,
          *
          * For each device that doesn't fit, disable it.
          */
-        fits = (base + region_size) <= BIT_ULL(pa_bits);
+        fits = (region_base + region_size) <= BIT_ULL(pa_bits);
         if (fits) {
-            vms->highest_gpa = base + region_size - 1;
+            vms->highest_gpa = region_base + region_size - 1;
         }
 
         switch (i) {
@@ -1726,7 +1726,7 @@ static void virt_set_high_memmap(VirtMachineState *vms,
             break;
         }
 
-        base += region_size;
+        base = region_base + region_size;
     }
 }
 
-- 
2.23.0

[PATCH v5 4/6] hw/arm/virt: Introduce virt_get_high_memmap_enabled() helper

[Gavin Shan]

This introduces virt_get_high_memmap_enabled() helper, which returns
the pointer to vms->highmem_{redists, ecam, mmio}. The pointer will
be used in the subsequent patches.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
---
 hw/arm/virt.c | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 0bf3cb7057..ee98a8a3b6 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1689,14 +1689,31 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
     return arm_cpu_mp_affinity(idx, clustersz);
 }
 
+static inline bool *virt_get_high_memmap_enabled(VirtMachineState *vms,
+                                                 int index)
+{
+    bool *enabled_array[] = {
+        &vms->highmem_redists,
+        &vms->highmem_ecam,
+        &vms->highmem_mmio,
+    };
+
+    assert(ARRAY_SIZE(extended_memmap) - VIRT_LOWMEMMAP_LAST ==
+           ARRAY_SIZE(enabled_array));
+    assert(index - VIRT_LOWMEMMAP_LAST < ARRAY_SIZE(enabled_array));
+
+    return enabled_array[index - VIRT_LOWMEMMAP_LAST];
+}
+
 static void virt_set_high_memmap(VirtMachineState *vms,
                                  hwaddr base, int pa_bits)
 {
     hwaddr region_base, region_size;
-    bool fits;
+    bool *region_enabled, fits;
     int i;
 
     for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
+        region_enabled = virt_get_high_memmap_enabled(vms, i);
         region_base = ROUND_UP(base, extended_memmap[i].size);
         region_size = extended_memmap[i].size;
 
@@ -1714,18 +1731,7 @@ static void virt_set_high_memmap(VirtMachineState *vms,
             vms->highest_gpa = region_base + region_size - 1;
         }
 
-        switch (i) {
-        case VIRT_HIGH_GIC_REDIST2:
-            vms->highmem_redists &= fits;
-            break;
-        case VIRT_HIGH_PCIE_ECAM:
-            vms->highmem_ecam &= fits;
-            break;
-        case VIRT_HIGH_PCIE_MMIO:
-            vms->highmem_mmio &= fits;
-            break;
-        }
-
+        *region_enabled &= fits;
         base = region_base + region_size;
     }
 }
-- 
2.23.0

[PATCH v5 5/6] hw/arm/virt: Improve high memory region address assignment

[Gavin Shan]

There are three high memory regions, which are VIRT_HIGH_REDIST2,
VIRT_HIGH_PCIE_ECAM and VIRT_HIGH_PCIE_MMIO. Their base addresses
are floating on highest RAM address. However, they can be disabled
in several cases.

(1) One specific high memory region is disabled by developer by
    toggling vms->highmem_{redists, ecam, mmio}.

(2) VIRT_HIGH_PCIE_ECAM region is disabled on machine, which is
    'virt-2.12' or ealier than it.

(3) VIRT_HIGH_PCIE_ECAM region is disabled when firmware is loaded
    on 32-bits system.

(4) One specific high memory region is disabled when it breaks the
    PA space limit.

The current implementation of virt_set_memmap() isn't comprehensive
because the space for one specific high memory region is always
reserved from the PA space for case (1), (2) and (3). In the code,
'base' and 'vms->highest_gpa' are always increased for those three
cases. It's unnecessary since the assigned space of the disabled
high memory region won't be used afterwards.

This improves the address assignment for those three high memory
region by skipping the address assignment for one specific high
memory region if it has been disabled in case (1), (2) and (3).
'vms->high_compact' is false for now, meaning that we don't have
any behavior changes until it becomes configurable through property
'compact-highmem' in next patch.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
---
 hw/arm/virt.c         | 23 +++++++++++++++--------
 include/hw/arm/virt.h |  1 +
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index ee98a8a3b6..c05cfb5314 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1717,22 +1717,29 @@ static void virt_set_high_memmap(VirtMachineState *vms,
         region_base = ROUND_UP(base, extended_memmap[i].size);
         region_size = extended_memmap[i].size;
 
-        vms->memmap[i].base = region_base;
-        vms->memmap[i].size = region_size;
-
         /*
          * Check each device to see if they fit in the PA space,
-         * moving highest_gpa as we go.
+         * moving highest_gpa as we go. For compatibility, move
+         * highest_gpa for disabled fitting devices as well, if
+         * the compact layout has been disabled.
          *
          * For each device that doesn't fit, disable it.
          */
         fits = (region_base + region_size) <= BIT_ULL(pa_bits);
-        if (fits) {
+        if (*region_enabled && fits) {
+            vms->memmap[i].base = region_base;
+            vms->memmap[i].size = region_size;
             vms->highest_gpa = region_base + region_size - 1;
+            base = region_base + region_size;
+        } else {
+            *region_enabled = false;
+            if (!vms->highmem_compact) {
+                base = region_base + region_size;
+                if (fits) {
+                    vms->highest_gpa = region_base + region_size - 1;
+                }
+            }
         }
-
-        *region_enabled &= fits;
-        base = region_base + region_size;
     }
 }
 
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 6ec479ca2b..709f623741 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -144,6 +144,7 @@ struct VirtMachineState {
     PFlashCFI01 *flash[2];
     bool secure;
     bool highmem;
+    bool highmem_compact;
     bool highmem_ecam;
     bool highmem_mmio;
     bool highmem_redists;
-- 
2.23.0

[PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Gavin Shan]

After the improvement to high memory region address assignment is
applied, the memory layout can be changed, introducing possible
migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
is disabled or enabled when the optimization is applied or not, with
the following configuration.

  pa_bits              = 40;
  vms->highmem_redists = false;
  vms->highmem_ecam    = false;
  vms->highmem_mmio    = true;

  # qemu-system-aarch64 -accel kvm -cpu host    \
    -machine virt-7.2,compact-highmem={on, off} \
    -m 4G,maxmem=511G -monitor stdio

  Region            compact-highmem=off         compact-highmem=on
  ----------------------------------------------------------------
  RAM               [1GB         512GB]        [1GB         512GB]
  HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
  HIGH_PCIE_ECAM    [512GB+256MB 512GB+512MB]  [disabled]
  HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]

In order to keep backwords compatibility, we need to disable the
optimization on machines, which is virt-7.1 or ealier than it. It
means the optimization is enabled by default from virt-7.2. Besides,
'compact-highmem' property is added so that the optimization can be
explicitly enabled or disabled on all machine types by users.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
---
 docs/system/arm/virt.rst |  4 ++++
 hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
 include/hw/arm/virt.h    |  1 +
 3 files changed, 52 insertions(+)

diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 20442ea2c1..75bf5a4994 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -94,6 +94,10 @@ highmem
   address space above 32 bits. The default is ``on`` for machine types
   later than ``virt-2.12``.
 
+compact-highmem
+  Set ``on``/``off`` to enable/disable compact space for high memory regions.
+  The default is ``on`` for machine types later than ``virt-7.2``
+
 gic-version
   Specify the version of the Generic Interrupt Controller (GIC) to provide.
   Valid values are:
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index c05cfb5314..8f1dba0ece 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -174,6 +174,27 @@ static const MemMapEntry base_memmap[] = {
  * Note the extended_memmap is sized so that it eventually also includes the
  * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
  * index of base_memmap).
+ *
+ * The addresses assigned to these regions are affected by 'compact-highmem'
+ * property, which is to enable or disable the compact space in the Highmem
+ * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
+ * depending on the property in the following scenario.
+ *
+ * pa_bits              = 40;
+ * vms->highmem_redists = false;
+ * vms->highmem_ecam    = false;
+ * vms->highmem_mmio    = true;
+ *
+ * # qemu-system-aarch64 -accel kvm -cpu host    \
+ *   -machine virt-7.2,compact-highmem={on, off} \
+ *   -m 4G,maxmem=511G -monitor stdio
+ *
+ * Region            compact-highmem=off        compact-highmem=on
+ * ----------------------------------------------------------------
+ * RAM               [1GB         512GB]        [1GB         512GB]
+ * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
+ * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
+ * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
  */
 static MemMapEntry extended_memmap[] = {
     /* Additional 64 MB redist region (can contain up to 512 redistributors) */
@@ -2353,6 +2374,20 @@ static void virt_set_highmem(Object *obj, bool value, Error **errp)
     vms->highmem = value;
 }
 
+static bool virt_get_compact_highmem(Object *obj, Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(obj);
+
+    return vms->highmem_compact;
+}
+
+static void virt_set_compact_highmem(Object *obj, bool value, Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(obj);
+
+    vms->highmem_compact = value;
+}
+
 static bool virt_get_its(Object *obj, Error **errp)
 {
     VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -2971,6 +3006,13 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
                                           "Set on/off to enable/disable using "
                                           "physical address space above 32 bits");
 
+    object_class_property_add_bool(oc, "compact-highmem",
+                                   virt_get_compact_highmem,
+                                   virt_set_compact_highmem);
+    object_class_property_set_description(oc, "compact-highmem",
+                                          "Set on/off to enable/disable compact "
+                                          "space for high memory regions");
+
     object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
                                   virt_set_gic_version);
     object_class_property_set_description(oc, "gic-version",
@@ -3055,6 +3097,7 @@ static void virt_instance_init(Object *obj)
 
     /* High memory is enabled by default */
     vms->highmem = true;
+    vms->highmem_compact = !vmc->no_highmem_compact;
     vms->gic_version = VIRT_GIC_VERSION_NOSEL;
 
     vms->highmem_ecam = !vmc->no_highmem_ecam;
@@ -3124,8 +3167,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
 
 static void virt_machine_7_1_options(MachineClass *mc)
 {
+    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
+
     virt_machine_7_2_options(mc);
     compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
+    /* Compact space for high memory regions was introduced with 7.2 */
+    vmc->no_highmem_compact = true;
 }
 DEFINE_VIRT_MACHINE(7, 1)
 
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 709f623741..c7dd59d7f1 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -125,6 +125,7 @@ struct VirtMachineClass {
     bool no_pmu;
     bool claim_edge_triggered_timers;
     bool smbios_old_sys_ver;
+    bool no_highmem_compact;
     bool no_highmem_ecam;
     bool no_ged;   /* Machines < 4.2 have no support for ACPI GED device */
     bool kvm_no_adjvtime;
-- 
2.23.0

Re: [PATCH v5 4/6] hw/arm/virt: Introduce virt_get_high_memmap_enabled() helper

[Cornelia Huck]

On Wed, Oct 12 2022, Gavin Shan <gshan@redhat.com> wrote:

> This introduces virt_get_high_memmap_enabled() helper, which returns
> the pointer to vms->highmem_{redists, ecam, mmio}. The pointer will
> be used in the subsequent patches.
>
> No functional change intended.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> ---
>  hw/arm/virt.c | 32 +++++++++++++++++++-------------
>  1 file changed, 19 insertions(+), 13 deletions(-)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

Re: [PATCH v5 5/6] hw/arm/virt: Improve high memory region address assignment

[Cornelia Huck]

On Wed, Oct 12 2022, Gavin Shan <gshan@redhat.com> wrote:

> There are three high memory regions, which are VIRT_HIGH_REDIST2,
> VIRT_HIGH_PCIE_ECAM and VIRT_HIGH_PCIE_MMIO. Their base addresses
> are floating on highest RAM address. However, they can be disabled
> in several cases.
>
> (1) One specific high memory region is disabled by developer by
>     toggling vms->highmem_{redists, ecam, mmio}.
>
> (2) VIRT_HIGH_PCIE_ECAM region is disabled on machine, which is
>     'virt-2.12' or ealier than it.
>
> (3) VIRT_HIGH_PCIE_ECAM region is disabled when firmware is loaded
>     on 32-bits system.
>
> (4) One specific high memory region is disabled when it breaks the
>     PA space limit.
>
> The current implementation of virt_set_memmap() isn't comprehensive
> because the space for one specific high memory region is always
> reserved from the PA space for case (1), (2) and (3). In the code,
> 'base' and 'vms->highest_gpa' are always increased for those three
> cases. It's unnecessary since the assigned space of the disabled
> high memory region won't be used afterwards.
>
> This improves the address assignment for those three high memory
> region by skipping the address assignment for one specific high
> memory region if it has been disabled in case (1), (2) and (3).
> 'vms->high_compact' is false for now, meaning that we don't have
> any behavior changes until it becomes configurable through property
> 'compact-highmem' in next patch.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> ---
>  hw/arm/virt.c         | 23 +++++++++++++++--------
>  include/hw/arm/virt.h |  1 +
>  2 files changed, 16 insertions(+), 8 deletions(-)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Cornelia Huck]

On Wed, Oct 12 2022, Gavin Shan <gshan@redhat.com> wrote:

> After the improvement to high memory region address assignment is
> applied, the memory layout can be changed, introducing possible
> migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
> is disabled or enabled when the optimization is applied or not, with
> the following configuration.
>
>   pa_bits              = 40;
>   vms->highmem_redists = false;
>   vms->highmem_ecam    = false;
>   vms->highmem_mmio    = true;
>
>   # qemu-system-aarch64 -accel kvm -cpu host    \
>     -machine virt-7.2,compact-highmem={on, off} \
>     -m 4G,maxmem=511G -monitor stdio
>
>   Region            compact-highmem=off         compact-highmem=on
>   ----------------------------------------------------------------
>   RAM               [1GB         512GB]        [1GB         512GB]
>   HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
>   HIGH_PCIE_ECAM    [512GB+256MB 512GB+512MB]  [disabled]
>   HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>
> In order to keep backwords compatibility, we need to disable the
> optimization on machines, which is virt-7.1 or ealier than it. It
> means the optimization is enabled by default from virt-7.2. Besides,
> 'compact-highmem' property is added so that the optimization can be
> explicitly enabled or disabled on all machine types by users.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> ---
>  docs/system/arm/virt.rst |  4 ++++
>  hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
>  include/hw/arm/virt.h    |  1 +
>  3 files changed, 52 insertions(+)
>
> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
> index 20442ea2c1..75bf5a4994 100644
> --- a/docs/system/arm/virt.rst
> +++ b/docs/system/arm/virt.rst
> @@ -94,6 +94,10 @@ highmem
>    address space above 32 bits. The default is ``on`` for machine types
>    later than ``virt-2.12``.
>  
> +compact-highmem
> +  Set ``on``/``off`` to enable/disable compact space for high memory regions.

Maybe s/compact space/the compact layout/ ?

> +  The default is ``on`` for machine types later than ``virt-7.2``
> +
>  gic-version
>    Specify the version of the Generic Interrupt Controller (GIC) to provide.
>    Valid values are:
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index c05cfb5314..8f1dba0ece 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -174,6 +174,27 @@ static const MemMapEntry base_memmap[] = {
>   * Note the extended_memmap is sized so that it eventually also includes the
>   * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
>   * index of base_memmap).
> + *
> + * The addresses assigned to these regions are affected by 'compact-highmem'
> + * property, which is to enable or disable the compact space in the Highmem

s/space in/layout for/ ?

> + * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
> + * depending on the property in the following scenario.
> + *
> + * pa_bits              = 40;
> + * vms->highmem_redists = false;
> + * vms->highmem_ecam    = false;
> + * vms->highmem_mmio    = true;
> + *
> + * # qemu-system-aarch64 -accel kvm -cpu host    \
> + *   -machine virt-7.2,compact-highmem={on, off} \
> + *   -m 4G,maxmem=511G -monitor stdio
> + *
> + * Region            compact-highmem=off        compact-highmem=on
> + * ----------------------------------------------------------------
> + * RAM               [1GB         512GB]        [1GB         512GB]
> + * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
> + * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
> + * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>   */
>  static MemMapEntry extended_memmap[] = {
>      /* Additional 64 MB redist region (can contain up to 512 redistributors) */

(...)

> @@ -3124,8 +3167,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
>  
>  static void virt_machine_7_1_options(MachineClass *mc)
>  {
> +    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
> +
>      virt_machine_7_2_options(mc);
>      compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
> +    /* Compact space for high memory regions was introduced with 7.2 */

s/space/layout/ ?

> +    vmc->no_highmem_compact = true;
>  }
>  DEFINE_VIRT_MACHINE(7, 1)
>  

Other than the wording nits, lgtm.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

Re: [PATCH v5 5/6] hw/arm/virt: Improve high memory region address assignment

[Eric Auger]

Hi Gavin

On 10/12/22 01:18, Gavin Shan wrote:
> There are three high memory regions, which are VIRT_HIGH_REDIST2,
> VIRT_HIGH_PCIE_ECAM and VIRT_HIGH_PCIE_MMIO. Their base addresses
> are floating on highest RAM address. However, they can be disabled
> in several cases.
>
> (1) One specific high memory region is disabled by developer by
>     toggling vms->highmem_{redists, ecam, mmio}.
I would replace the above sentence by

One specific high memory region is likely to be disabled by the code by toggling vms->highmem_{redists, ecam, mmio}:

>
> (2) VIRT_HIGH_PCIE_ECAM region is disabled on machine, which is
>     'virt-2.12' or ealier than it.
>
> (3) VIRT_HIGH_PCIE_ECAM region is disabled when firmware is loaded
>     on 32-bits system.
>
> (4) One specific high memory region is disabled when it breaks the
>     PA space limit.
>
> The current implementation of virt_set_memmap() isn't comprehensive
> because the space for one specific high memory region is always
> reserved from the PA space for case (1), (2) and (3).
I would suggest:
isn't optimized because the high memory region PA range is always

reserved whatever the actual state of the corresponding vms->highmem_
* flag.

>  In the code,
> 'base' and 'vms->highest_gpa' are always increased for those three
> cases. It's unnecessary since the assigned space of the disabled
> high memory region won't be used afterwards.
>
> This improves the address assignment for those three high memory
s/This improves/Improve
> region by skipping the address assignment for one specific high
> memory region if it has been disabled in case (1), (2) and (3).
> 'vms->high_compact' is false for now, meaning that we don't have
s/hight_compat/highmem_compact

You also may justify the introduction of this new field.
> any behavior changes until it becomes configurable through property
> 'compact-highmem' in next patch.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> ---
>  hw/arm/virt.c         | 23 +++++++++++++++--------
>  include/hw/arm/virt.h |  1 +
>  2 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index ee98a8a3b6..c05cfb5314 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1717,22 +1717,29 @@ static void virt_set_high_memmap(VirtMachineState *vms,
>          region_base = ROUND_UP(base, extended_memmap[i].size);
>          region_size = extended_memmap[i].size;
>  
> -        vms->memmap[i].base = region_base;
> -        vms->memmap[i].size = region_size;
> -
>          /*
>           * Check each device to see if they fit in the PA space,
while we are at it, you can change s/they fit/it fits
> -         * moving highest_gpa as we go.
> +         * moving highest_gpa as we go. For compatibility, move
> +         * highest_gpa for disabled fitting devices as well, if
> +         * the compact layout has been disabled.
>           *
>           * For each device that doesn't fit, disable it.
>           */
>          fits = (region_base + region_size) <= BIT_ULL(pa_bits);
> -        if (fits) {
> +        if (*region_enabled && fits) {
> +            vms->memmap[i].base = region_base;
> +            vms->memmap[i].size = region_size;
>              vms->highest_gpa = region_base + region_size - 1;
> +            base = region_base + region_size;
> +        } else {
> +            *region_enabled = false;
> +            if (!vms->highmem_compact) {
> +                base = region_base + region_size;
> +                if (fits) {
> +                    vms->highest_gpa = region_base + region_size - 1;
> +                }
> +            }
>          }
> -
> -        *region_enabled &= fits;
> -        base = region_base + region_size;
>      }
>  }
This looks quite complicated to me. It is not obvious for instance we
have the same code as before when highmem_compact is not set. Typically

vms->memmap[i].base/size are not always set as they were to be and impact on the rest of the code must be double checked.

Could this be rewritten in that way (pseudocode totally untested).


static void fit_highmem_slot(vms, *base, i, pa_bits)
{
    region_enabled = virt_get_high_memmap_enabled(vms, i);
    region_base = ROUND_UP(*base, extended_memmap[i].size);
    region_size = extended_memmap[i].size;
    fits = (region_base + region_size) <= BIT_ULL(pa_bits);
    *region_enabled &= fits;
    vms->memmap[i].base = region_base;
    vms->memmap[i].size = region_size;

    /* compact layout only allocates space for the region if this latter
is enabled & fits*/
    if (vms->highmem_compact && !region_enabled) {
        return;
    }

    /* account for the region and update the base address/highest_gpa if
needed*/ 
    *base = region_base + region_size;
    if (fits) { 
        vms->highest_gpa = *base - 1;
    }
}

static void virt_set_high_memmap(VirtMachineState *vms,
                                 hwaddr base, int pa_bits)
{
    hwaddr region_base, region_size;
    bool *region_enabled, fits;
    int i;

    for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
        /* we do not break in case the region does not fit since
fit_highmem_slot also updates the enabled status of the region */
        fit_highmem_slot(vms, &base, i, pa_bits);
    }
}

>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 6ec479ca2b..709f623741 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -144,6 +144,7 @@ struct VirtMachineState {
>      PFlashCFI01 *flash[2];
>      bool secure;
>      bool highmem;
> +    bool highmem_compact;
>      bool highmem_ecam;
>      bool highmem_mmio;
>      bool highmem_redists;
Thanks

Eric

Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Eric Auger]

Hi Gavin,

On 10/12/22 01:18, Gavin Shan wrote:
> After the improvement to high memory region address assignment is
> applied, the memory layout can be changed, introducing possible
> migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
> is disabled or enabled when the optimization is applied or not, with
> the following configuration.
>
>   pa_bits              = 40;
>   vms->highmem_redists = false;
>   vms->highmem_ecam    = false;
>   vms->highmem_mmio    = true;
>
>   # qemu-system-aarch64 -accel kvm -cpu host    \
>     -machine virt-7.2,compact-highmem={on, off} \
>     -m 4G,maxmem=511G -monitor stdio
>
>   Region            compact-highmem=off         compact-highmem=on
>   ----------------------------------------------------------------
>   RAM               [1GB         512GB]        [1GB         512GB]
>   HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
>   HIGH_PCIE_ECAM    [512GB+256MB 512GB+512MB]  [disabled]
>   HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>
> In order to keep backwords compatibility, we need to disable the
> optimization on machines, which is virt-7.1 or ealier than it. It
> means the optimization is enabled by default from virt-7.2. Besides,
> 'compact-highmem' property is added so that the optimization can be
> explicitly enabled or disabled on all machine types by users.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
> ---
>  docs/system/arm/virt.rst |  4 ++++
>  hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
>  include/hw/arm/virt.h    |  1 +
>  3 files changed, 52 insertions(+)
>
> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
> index 20442ea2c1..75bf5a4994 100644
> --- a/docs/system/arm/virt.rst
> +++ b/docs/system/arm/virt.rst
> @@ -94,6 +94,10 @@ highmem
>    address space above 32 bits. The default is ``on`` for machine types
>    later than ``virt-2.12``.
>  
> +compact-highmem
> +  Set ``on``/``off`` to enable/disable compact space for high memory regions.
> +  The default is ``on`` for machine types later than ``virt-7.2``
> +
>  gic-version
>    Specify the version of the Generic Interrupt Controller (GIC) to provide.
>    Valid values are:
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index c05cfb5314..8f1dba0ece 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -174,6 +174,27 @@ static const MemMapEntry base_memmap[] = {
>   * Note the extended_memmap is sized so that it eventually also includes the
>   * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
>   * index of base_memmap).
> + *
> + * The addresses assigned to these regions are affected by 'compact-highmem'
> + * property, which is to enable or disable the compact space in the Highmem
> + * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
> + * depending on the property in the following scenario.
To me you shall rather explain here what is the so-called "compact"
space vs the legacy highmem layout.

If I understand correctly the example rather legitimates the use of a
compat option showing how the layout can be affected by the option. I
would put that in the commit msg instead. Also in your example I see
VIRT_HIGH_GIC_REDISTS is disabled but the code does not disable the
region excpet if it does not fit within the PA. This does not match your
example. Also the region is named VIRT_HIGH_GIC_REDIST2.

In v4, Marc also suggested to have individual options for each highmem
region.
https://lore.kernel.org/qemu-devel/0f8e6a58-0dde-fb80-6966-7bb32c4df552@redhat.com/

Have you considered that option?

Thanks

Eric
> + *
> + * pa_bits              = 40;
> + * vms->highmem_redists = false;
> + * vms->highmem_ecam    = false;
> + * vms->highmem_mmio    = true;
> + *
> + * # qemu-system-aarch64 -accel kvm -cpu host    \
> + *   -machine virt-7.2,compact-highmem={on, off} \
> + *   -m 4G,maxmem=511G -monitor stdio
> + *
> + * Region            compact-highmem=off        compact-highmem=on
> + * ----------------------------------------------------------------
> + * RAM               [1GB         512GB]        [1GB         512GB]
> + * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
> + * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
> + * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>   */
>  static MemMapEntry extended_memmap[] = {
>      /* Additional 64 MB redist region (can contain up to 512 redistributors) */
> @@ -2353,6 +2374,20 @@ static void virt_set_highmem(Object *obj, bool value, Error **errp)
>      vms->highmem = value;
>  }
>  
> +static bool virt_get_compact_highmem(Object *obj, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    return vms->highmem_compact;
> +}
> +
> +static void virt_set_compact_highmem(Object *obj, bool value, Error **errp)
> +{
> +    VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +    vms->highmem_compact = value;
> +}
> +
>  static bool virt_get_its(Object *obj, Error **errp)
>  {
>      VirtMachineState *vms = VIRT_MACHINE(obj);
> @@ -2971,6 +3006,13 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
>                                            "Set on/off to enable/disable using "
>                                            "physical address space above 32 bits");
>  
> +    object_class_property_add_bool(oc, "compact-highmem",
> +                                   virt_get_compact_highmem,
> +                                   virt_set_compact_highmem);
> +    object_class_property_set_description(oc, "compact-highmem",
> +                                          "Set on/off to enable/disable compact "
> +                                          "space for high memory regions");
> +
>      object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
>                                    virt_set_gic_version);
>      object_class_property_set_description(oc, "gic-version",
> @@ -3055,6 +3097,7 @@ static void virt_instance_init(Object *obj)
>  
>      /* High memory is enabled by default */
>      vms->highmem = true;
> +    vms->highmem_compact = !vmc->no_highmem_compact;
>      vms->gic_version = VIRT_GIC_VERSION_NOSEL;
>  
>      vms->highmem_ecam = !vmc->no_highmem_ecam;
> @@ -3124,8 +3167,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
>  
>  static void virt_machine_7_1_options(MachineClass *mc)
>  {
> +    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
> +
>      virt_machine_7_2_options(mc);
>      compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
> +    /* Compact space for high memory regions was introduced with 7.2 */
> +    vmc->no_highmem_compact = true;
>  }
>  DEFINE_VIRT_MACHINE(7, 1)
>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 709f623741..c7dd59d7f1 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -125,6 +125,7 @@ struct VirtMachineClass {
>      bool no_pmu;
>      bool claim_edge_triggered_timers;
>      bool smbios_old_sys_ver;
> +    bool no_highmem_compact;
>      bool no_highmem_ecam;
>      bool no_ged;   /* Machines < 4.2 have no support for ACPI GED device */
>      bool kvm_no_adjvtime;

Re: [PATCH v5 5/6] hw/arm/virt: Improve high memory region address assignment

[Gavin Shan]

Hi Eric,

On 10/20/22 4:07 AM, Eric Auger wrote:
> On 10/12/22 01:18, Gavin Shan wrote:
>> There are three high memory regions, which are VIRT_HIGH_REDIST2,
>> VIRT_HIGH_PCIE_ECAM and VIRT_HIGH_PCIE_MMIO. Their base addresses
>> are floating on highest RAM address. However, they can be disabled
>> in several cases.
>>
>> (1) One specific high memory region is disabled by developer by
>>      toggling vms->highmem_{redists, ecam, mmio}.
> I would replace the above sentence by
> 
> One specific high memory region is likely to be disabled by the code by toggling vms->highmem_{redists, ecam, mmio}:
> 

Ok.

>>
>> (2) VIRT_HIGH_PCIE_ECAM region is disabled on machine, which is
>>      'virt-2.12' or ealier than it.
>>
>> (3) VIRT_HIGH_PCIE_ECAM region is disabled when firmware is loaded
>>      on 32-bits system.
>>
>> (4) One specific high memory region is disabled when it breaks the
>>      PA space limit.
>>
>> The current implementation of virt_set_memmap() isn't comprehensive
>> because the space for one specific high memory region is always
>> reserved from the PA space for case (1), (2) and (3).
> I would suggest:
> isn't optimized because the high memory region PA range is always
> 
> reserved whatever the actual state of the corresponding vms->highmem_
> * flag.
> 

Ok. I will have something like below in next revision.

   The current implementation of virt_set_{memmap, high_memmap}() isn't
   optimized because the high memory region's PA space is always reserved,
   regardless of whatever the actual state in the corresponding
   vms->highmem_{redists, ecam, mmio} flag. In the code, ....

>>   In the code,
>> 'base' and 'vms->highest_gpa' are always increased for those three
>> cases. It's unnecessary since the assigned space of the disabled
>> high memory region won't be used afterwards.
>>
>> This improves the address assignment for those three high memory
> s/This improves/Improve

Ok.

>> region by skipping the address assignment for one specific high
>> memory region if it has been disabled in case (1), (2) and (3).
>> 'vms->high_compact' is false for now, meaning that we don't have
> s/hight_compat/highmem_compact
> 
> You also may justify the introduction of this new field.

Thanks. It should be 'highmem_compact'. Yes, it makes sense to
justify the addition of 'vms->highmem_compact'. I will have something
like below in next revision.

   The memory layout may be changed after the improvement is applied, which
   leads to potential migration breakage. So 'vms->highmem_compact' is added
   to control if the improvement should be applied. For now, 'vms->highmem_compact'
   is set to false, meaning that we don't have memory layout change until it
   becomes configurable through property 'compact-highmem' in next patch.

>> any behavior changes until it becomes configurable through property
>> 'compact-highmem' in next patch.
>>>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
>> ---
>>   hw/arm/virt.c         | 23 +++++++++++++++--------
>>   include/hw/arm/virt.h |  1 +
>>   2 files changed, 16 insertions(+), 8 deletions(-)
>>
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index ee98a8a3b6..c05cfb5314 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -1717,22 +1717,29 @@ static void virt_set_high_memmap(VirtMachineState *vms,
>>           region_base = ROUND_UP(base, extended_memmap[i].size);
>>           region_size = extended_memmap[i].size;
>>   
>> -        vms->memmap[i].base = region_base;
>> -        vms->memmap[i].size = region_size;
>> -
>>           /*
>>            * Check each device to see if they fit in the PA space,
> while we are at it, you can change s/they fit/it fits

Agreed.

>> -         * moving highest_gpa as we go.
>> +         * moving highest_gpa as we go. For compatibility, move
>> +         * highest_gpa for disabled fitting devices as well, if
>> +         * the compact layout has been disabled.
>>            *
>>            * For each device that doesn't fit, disable it.
>>            */
>>           fits = (region_base + region_size) <= BIT_ULL(pa_bits);
>> -        if (fits) {
>> +        if (*region_enabled && fits) {
>> +            vms->memmap[i].base = region_base;
>> +            vms->memmap[i].size = region_size;
>>               vms->highest_gpa = region_base + region_size - 1;
>> +            base = region_base + region_size;
>> +        } else {
>> +            *region_enabled = false;
>> +            if (!vms->highmem_compact) {
>> +                base = region_base + region_size;
>> +                if (fits) {
>> +                    vms->highest_gpa = region_base + region_size - 1;
>> +                }
>> +            }
>>           }
>> -
>> -        *region_enabled &= fits;
>> -        base = region_base + region_size;
>>       }
>>   }
> This looks quite complicated to me. It is not obvious for instance we
> have the same code as before when highmem_compact is not set. Typically
> 
> vms->memmap[i].base/size are not always set as they were to be and impact on the rest of the code must be double checked.
> 
> Could this be rewritten in that way (pseudocode totally untested).
> 
> 
> static void fit_highmem_slot(vms, *base, i, pa_bits)
> {
>      region_enabled = virt_get_high_memmap_enabled(vms, i);
>      region_base = ROUND_UP(*base, extended_memmap[i].size);
>      region_size = extended_memmap[i].size;
>      fits = (region_base + region_size) <= BIT_ULL(pa_bits);
>      *region_enabled &= fits;
>      vms->memmap[i].base = region_base;
>      vms->memmap[i].size = region_size;
> 
>      /* compact layout only allocates space for the region if this latter
> is enabled & fits*/
>      if (vms->highmem_compact && !region_enabled) {
>          return;
>      }
> 
>      /* account for the region and update the base address/highest_gpa if
> needed*/
>      *base = region_base + region_size;
>      if (fits) {
>          vms->highest_gpa = *base - 1;
>      }
> }
> 
> static void virt_set_high_memmap(VirtMachineState *vms,
>                                   hwaddr base, int pa_bits)
> {
>      hwaddr region_base, region_size;
>      bool *region_enabled, fits;
>      int i;
> 
>      for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
>          /* we do not break in case the region does not fit since
> fit_highmem_slot also updates the enabled status of the region */
>          fit_highmem_slot(vms, &base, i, pa_bits);
>      }
> }
> 
>>   
>> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
>> index 6ec479ca2b..709f623741 100644
>> --- a/include/hw/arm/virt.h
>> +++ b/include/hw/arm/virt.h
>> @@ -144,6 +144,7 @@ struct VirtMachineState {
>>       PFlashCFI01 *flash[2];
>>       bool secure;
>>       bool highmem;
>> +    bool highmem_compact;
>>       bool highmem_ecam;
>>       bool highmem_mmio;
>>       bool highmem_redists;

I checked it again. When the corresponding high memory region is disabled, skipping to
setting vms->memmap[i].base/size won't affect the left code.

I would avoid introducing another helper here, meaning I want to squeeze everything
into existing virt_set_high_memmap(). With additional helper, there are too many
function calls in the stack to accomplish this sort of simple task (address assignment
for high memory regions). Without the additional helper, the changes can be simply as
below.

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index ee98a8a3b6..da9e23a8ad 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1721,18 +1721,23 @@ static void virt_set_high_memmap(VirtMachineState *vms,
          vms->memmap[i].size = region_size;
  
          /*
-         * Check each device to see if they fit in the PA space,
-         * moving highest_gpa as we go.
+         * Check each device to see if it fits in the PA space,
+         * moving highest_gpa as we go. For compatibility, move
+         * highest_gpa for disabled fitting devices as well, if
+         * the compact layout has been disabled.
           *
           * For each device that doesn't fit, disable it.
           */
          fits = (region_base + region_size) <= BIT_ULL(pa_bits);
-        if (fits) {
-            vms->highest_gpa = region_base + region_size - 1;
+        *region_enabled &= fits;
+        if (vms->highmem_compact && !*region_enabled) {
+            continue;
          }
  
-        *region_enabled &= fits;
          base = region_base + region_size;
+       if (fits) {
+               vms->highest_gpa = region_base + region_size - 1;
+       }
      }
  }

Thanks,
Gavin

Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Gavin Shan]

Hi Connie,

On 10/19/22 10:00 PM, Cornelia Huck wrote:
> On Wed, Oct 12 2022, Gavin Shan <gshan@redhat.com> wrote:
> 
>> After the improvement to high memory region address assignment is
>> applied, the memory layout can be changed, introducing possible
>> migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
>> is disabled or enabled when the optimization is applied or not, with
>> the following configuration.
>>
>>    pa_bits              = 40;
>>    vms->highmem_redists = false;
>>    vms->highmem_ecam    = false;
>>    vms->highmem_mmio    = true;
>>
>>    # qemu-system-aarch64 -accel kvm -cpu host    \
>>      -machine virt-7.2,compact-highmem={on, off} \
>>      -m 4G,maxmem=511G -monitor stdio
>>
>>    Region            compact-highmem=off         compact-highmem=on
>>    ----------------------------------------------------------------
>>    RAM               [1GB         512GB]        [1GB         512GB]
>>    HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
>>    HIGH_PCIE_ECAM    [512GB+256MB 512GB+512MB]  [disabled]
>>    HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>>
>> In order to keep backwords compatibility, we need to disable the
>> optimization on machines, which is virt-7.1 or ealier than it. It
>> means the optimization is enabled by default from virt-7.2. Besides,
>> 'compact-highmem' property is added so that the optimization can be
>> explicitly enabled or disabled on all machine types by users.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
>> ---
>>   docs/system/arm/virt.rst |  4 ++++
>>   hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
>>   include/hw/arm/virt.h    |  1 +
>>   3 files changed, 52 insertions(+)
>>
>> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
>> index 20442ea2c1..75bf5a4994 100644
>> --- a/docs/system/arm/virt.rst
>> +++ b/docs/system/arm/virt.rst
>> @@ -94,6 +94,10 @@ highmem
>>     address space above 32 bits. The default is ``on`` for machine types
>>     later than ``virt-2.12``.
>>   
>> +compact-highmem
>> +  Set ``on``/``off`` to enable/disable compact space for high memory regions.
> 
> Maybe s/compact space/the compact layout/ ?
> 

Yeah, 'compact layout' is better. I will amend in next respin.

>> +  The default is ``on`` for machine types later than ``virt-7.2``
>> +
>>   gic-version
>>     Specify the version of the Generic Interrupt Controller (GIC) to provide.
>>     Valid values are:
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index c05cfb5314..8f1dba0ece 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -174,6 +174,27 @@ static const MemMapEntry base_memmap[] = {
>>    * Note the extended_memmap is sized so that it eventually also includes the
>>    * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
>>    * index of base_memmap).
>> + *
>> + * The addresses assigned to these regions are affected by 'compact-highmem'
>> + * property, which is to enable or disable the compact space in the Highmem
> 
> s/space in/layout for/ ?
> 

Agreed.

>> + * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
>> + * depending on the property in the following scenario.
>> + *
>> + * pa_bits              = 40;
>> + * vms->highmem_redists = false;
>> + * vms->highmem_ecam    = false;
>> + * vms->highmem_mmio    = true;
>> + *
>> + * # qemu-system-aarch64 -accel kvm -cpu host    \
>> + *   -machine virt-7.2,compact-highmem={on, off} \
>> + *   -m 4G,maxmem=511G -monitor stdio
>> + *
>> + * Region            compact-highmem=off        compact-highmem=on
>> + * ----------------------------------------------------------------
>> + * RAM               [1GB         512GB]        [1GB         512GB]
>> + * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
>> + * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
>> + * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>>    */
>>   static MemMapEntry extended_memmap[] = {
>>       /* Additional 64 MB redist region (can contain up to 512 redistributors) */
> 
> (...)
> 
>> @@ -3124,8 +3167,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
>>   
>>   static void virt_machine_7_1_options(MachineClass *mc)
>>   {
>> +    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
>> +
>>       virt_machine_7_2_options(mc);
>>       compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
>> +    /* Compact space for high memory regions was introduced with 7.2 */
> 
> s/space/layout/ ?
> 

Ack.

>> +    vmc->no_highmem_compact = true;
>>   }
>>   DEFINE_VIRT_MACHINE(7, 1)
>>   
> 
> Other than the wording nits, lgtm.
> 
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> 

Thanks,
Gavin

Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Gavin Shan]

Hi Eric,

On 10/20/22 4:18 AM, Eric Auger wrote:
> On 10/12/22 01:18, Gavin Shan wrote:
>> After the improvement to high memory region address assignment is
>> applied, the memory layout can be changed, introducing possible
>> migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
>> is disabled or enabled when the optimization is applied or not, with
>> the following configuration.
>>
>>    pa_bits              = 40;
>>    vms->highmem_redists = false;
>>    vms->highmem_ecam    = false;
>>    vms->highmem_mmio    = true;
>>
>>    # qemu-system-aarch64 -accel kvm -cpu host    \
>>      -machine virt-7.2,compact-highmem={on, off} \
>>      -m 4G,maxmem=511G -monitor stdio
>>
>>    Region            compact-highmem=off         compact-highmem=on
>>    ----------------------------------------------------------------
>>    RAM               [1GB         512GB]        [1GB         512GB]
>>    HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
>>    HIGH_PCIE_ECAM    [512GB+256MB 512GB+512MB]  [disabled]
>>    HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>>
>> In order to keep backwords compatibility, we need to disable the
>> optimization on machines, which is virt-7.1 or ealier than it. It
>> means the optimization is enabled by default from virt-7.2. Besides,
>> 'compact-highmem' property is added so that the optimization can be
>> explicitly enabled or disabled on all machine types by users.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
>> ---
>>   docs/system/arm/virt.rst |  4 ++++
>>   hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
>>   include/hw/arm/virt.h    |  1 +
>>   3 files changed, 52 insertions(+)
>>
>> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
>> index 20442ea2c1..75bf5a4994 100644
>> --- a/docs/system/arm/virt.rst
>> +++ b/docs/system/arm/virt.rst
>> @@ -94,6 +94,10 @@ highmem
>>     address space above 32 bits. The default is ``on`` for machine types
>>     later than ``virt-2.12``.
>>   
>> +compact-highmem
>> +  Set ``on``/``off`` to enable/disable compact space for high memory regions.
>> +  The default is ``on`` for machine types later than ``virt-7.2``
>> +
>>   gic-version
>>     Specify the version of the Generic Interrupt Controller (GIC) to provide.
>>     Valid values are:
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index c05cfb5314..8f1dba0ece 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -174,6 +174,27 @@ static const MemMapEntry base_memmap[] = {
>>    * Note the extended_memmap is sized so that it eventually also includes the
>>    * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
>>    * index of base_memmap).
>> + *
>> + * The addresses assigned to these regions are affected by 'compact-highmem'
>> + * property, which is to enable or disable the compact space in the Highmem
>> + * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
>> + * depending on the property in the following scenario.
> To me you shall rather explain here what is the so-called "compact"
> space vs the legacy highmem layout.
> 
> If I understand correctly the example rather legitimates the use of a
> compat option showing how the layout can be affected by the option. I
> would put that in the commit msg instead. Also in your example I see
> VIRT_HIGH_GIC_REDISTS is disabled but the code does not disable the
> region excpet if it does not fit within the PA. This does not match your
> example. Also the region is named VIRT_HIGH_GIC_REDIST2.
> 
> In v4, Marc also suggested to have individual options for each highmem
> region.
> https://lore.kernel.org/qemu-devel/0f8e6a58-0dde-fb80-6966-7bb32c4df552@redhat.com/
> 
> Have you considered that option?
> 

I think your comments make sense to me. So lets put the following comments
to the code and move the example to commit log.

   /*
    * The memory map for these Highmem IO Regions can be in legacy or compact
    * layout, depending on 'compact-highmem' property. In legacy layout, the
    * PA space for one specific region is always reserved, even the region has
    * been disabled or doesn't fit into the PA space. However, the PA space for
    * the region won't be reserved in these circumstances.
    */

You're correct about the example. VIRT_HIGH_GIC_REDIST2 should be used. Besides,
the configuration is only achievable by modifying source code at present, until
Marc's suggestion rolls in to allow users disable one particular high memory
regions by more properties. I will amend the commit log to have something like
below.

     For example, VIRT_HIGH_PCIE_MMIO memory region is disabled or enabled when
     the optimization is applied or not, with the following configuration. The
     configuration is only achievable by modifying source code, until more properties
     are added to allow user selectively disable those high memory regions.

For Marc's suggestion to add properties so that these high memory regions can
be disabled by users. I can add one patch after this one to introduce the following
3 properties. Could you please confirm the property names are good enough? It's
nice if Marc can help to confirm before I'm going to work on next revision.

     "highmem-ecam":    "on"/"off" on vms->highmem_ecam
     "highmem-mmio":    "on"/"off" on vms->highmem_mmio
     "highmem-redists": "on"/"off" on vms->highmem_redists

>> + *
>> + * pa_bits              = 40;
>> + * vms->highmem_redists = false;
>> + * vms->highmem_ecam    = false;
>> + * vms->highmem_mmio    = true;
>> + *
>> + * # qemu-system-aarch64 -accel kvm -cpu host    \
>> + *   -machine virt-7.2,compact-highmem={on, off} \
>> + *   -m 4G,maxmem=511G -monitor stdio
>> + *
>> + * Region            compact-highmem=off        compact-highmem=on
>> + * ----------------------------------------------------------------
>> + * RAM               [1GB         512GB]        [1GB         512GB]
>> + * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
>> + * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
>> + * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
>>    */
>>   static MemMapEntry extended_memmap[] = {
>>       /* Additional 64 MB redist region (can contain up to 512 redistributors) */
>> @@ -2353,6 +2374,20 @@ static void virt_set_highmem(Object *obj, bool value, Error **errp)
>>       vms->highmem = value;
>>   }
>>   
>> +static bool virt_get_compact_highmem(Object *obj, Error **errp)
>> +{
>> +    VirtMachineState *vms = VIRT_MACHINE(obj);
>> +
>> +    return vms->highmem_compact;
>> +}
>> +
>> +static void virt_set_compact_highmem(Object *obj, bool value, Error **errp)
>> +{
>> +    VirtMachineState *vms = VIRT_MACHINE(obj);
>> +
>> +    vms->highmem_compact = value;
>> +}
>> +
>>   static bool virt_get_its(Object *obj, Error **errp)
>>   {
>>       VirtMachineState *vms = VIRT_MACHINE(obj);
>> @@ -2971,6 +3006,13 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
>>                                             "Set on/off to enable/disable using "
>>                                             "physical address space above 32 bits");
>>   
>> +    object_class_property_add_bool(oc, "compact-highmem",
>> +                                   virt_get_compact_highmem,
>> +                                   virt_set_compact_highmem);
>> +    object_class_property_set_description(oc, "compact-highmem",
>> +                                          "Set on/off to enable/disable compact "
>> +                                          "space for high memory regions");
>> +
>>       object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
>>                                     virt_set_gic_version);
>>       object_class_property_set_description(oc, "gic-version",
>> @@ -3055,6 +3097,7 @@ static void virt_instance_init(Object *obj)
>>   
>>       /* High memory is enabled by default */
>>       vms->highmem = true;
>> +    vms->highmem_compact = !vmc->no_highmem_compact;
>>       vms->gic_version = VIRT_GIC_VERSION_NOSEL;
>>   
>>       vms->highmem_ecam = !vmc->no_highmem_ecam;
>> @@ -3124,8 +3167,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
>>   
>>   static void virt_machine_7_1_options(MachineClass *mc)
>>   {
>> +    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
>> +
>>       virt_machine_7_2_options(mc);
>>       compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
>> +    /* Compact space for high memory regions was introduced with 7.2 */
>> +    vmc->no_highmem_compact = true;
>>   }
>>   DEFINE_VIRT_MACHINE(7, 1)
>>   
>> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
>> index 709f623741..c7dd59d7f1 100644
>> --- a/include/hw/arm/virt.h
>> +++ b/include/hw/arm/virt.h
>> @@ -125,6 +125,7 @@ struct VirtMachineClass {
>>       bool no_pmu;
>>       bool claim_edge_triggered_timers;
>>       bool smbios_old_sys_ver;
>> +    bool no_highmem_compact;
>>       bool no_highmem_ecam;
>>       bool no_ged;   /* Machines < 4.2 have no support for ACPI GED device */
>>       bool kvm_no_adjvtime;
> 

Thanks,
Gavin

Re: [PATCH v5 4/6] hw/arm/virt: Introduce virt_get_high_memmap_enabled() helper

[Eric Auger]

On 10/12/22 01:18, Gavin Shan wrote:
> This introduces virt_get_high_memmap_enabled() helper, which returns
> the pointer to vms->highmem_{redists, ecam, mmio}. The pointer will
> be used in the subsequent patches.
>
> No functional change intended.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>


Eric
> ---
>  hw/arm/virt.c | 32 +++++++++++++++++++-------------
>  1 file changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 0bf3cb7057..ee98a8a3b6 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1689,14 +1689,31 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
>      return arm_cpu_mp_affinity(idx, clustersz);
>  }
>  
> +static inline bool *virt_get_high_memmap_enabled(VirtMachineState *vms,
> +                                                 int index)
> +{
> +    bool *enabled_array[] = {
> +        &vms->highmem_redists,
> +        &vms->highmem_ecam,
> +        &vms->highmem_mmio,
> +    };
> +
> +    assert(ARRAY_SIZE(extended_memmap) - VIRT_LOWMEMMAP_LAST ==
> +           ARRAY_SIZE(enabled_array));
> +    assert(index - VIRT_LOWMEMMAP_LAST < ARRAY_SIZE(enabled_array));
> +
> +    return enabled_array[index - VIRT_LOWMEMMAP_LAST];
> +}
> +
>  static void virt_set_high_memmap(VirtMachineState *vms,
>                                   hwaddr base, int pa_bits)
>  {
>      hwaddr region_base, region_size;
> -    bool fits;
> +    bool *region_enabled, fits;
>      int i;
>  
>      for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
> +        region_enabled = virt_get_high_memmap_enabled(vms, i);
>          region_base = ROUND_UP(base, extended_memmap[i].size);
>          region_size = extended_memmap[i].size;
>  
> @@ -1714,18 +1731,7 @@ static void virt_set_high_memmap(VirtMachineState *vms,
>              vms->highest_gpa = region_base + region_size - 1;
>          }
>  
> -        switch (i) {
> -        case VIRT_HIGH_GIC_REDIST2:
> -            vms->highmem_redists &= fits;
> -            break;
> -        case VIRT_HIGH_PCIE_ECAM:
> -            vms->highmem_ecam &= fits;
> -            break;
> -        case VIRT_HIGH_PCIE_MMIO:
> -            vms->highmem_mmio &= fits;
> -            break;
> -        }
> -
> +        *region_enabled &= fits;
>          base = region_base + region_size;
>      }
>  }

Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Marc Zyngier]

On Thu, 20 Oct 2022 00:57:32 +0100,
Gavin Shan <gshan@redhat.com> wrote:
> 
> For Marc's suggestion to add properties so that these high memory
> regions can be disabled by users. I can add one patch after this one
> to introduce the following 3 properties. Could you please confirm
> the property names are good enough? It's nice if Marc can help to
> confirm before I'm going to work on next revision.
> 
>     "highmem-ecam":    "on"/"off" on vms->highmem_ecam
>     "highmem-mmio":    "on"/"off" on vms->highmem_mmio
>     "highmem-redists": "on"/"off" on vms->highmem_redists

I think that'd be reasonable, and would give the user some actual
control over what gets exposed in the highmem region.

I guess that the annoying thing with these options is that they allow
the user to request conflicting settings (256 CPUs and
highmem-redists=off, for example). You'll need to make this fail more
or less gracefully.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Gavin Shan]

Hi Marc,

On 10/20/22 5:44 PM, Marc Zyngier wrote:
> On Thu, 20 Oct 2022 00:57:32 +0100,
> Gavin Shan <gshan@redhat.com> wrote:
>>
>> For Marc's suggestion to add properties so that these high memory
>> regions can be disabled by users. I can add one patch after this one
>> to introduce the following 3 properties. Could you please confirm
>> the property names are good enough? It's nice if Marc can help to
>> confirm before I'm going to work on next revision.
>>
>>      "highmem-ecam":    "on"/"off" on vms->highmem_ecam
>>      "highmem-mmio":    "on"/"off" on vms->highmem_mmio
>>      "highmem-redists": "on"/"off" on vms->highmem_redists
> 
> I think that'd be reasonable, and would give the user some actual
> control over what gets exposed in the highmem region.
> 
> I guess that the annoying thing with these options is that they allow
> the user to request conflicting settings (256 CPUs and
> highmem-redists=off, for example). You'll need to make this fail more
> or less gracefully.
> 

Thanks for the quick confirm. The check is already existing in machvirt_init().
I think what we need is simply to calculate 'virt_max_cpus' with consideration
to 'highmem-redists' property there.

     if (max_cpus > virt_max_cpus) {
         error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
                      "supported by machine 'mach-virt' (%d)",
                      max_cpus, virt_max_cpus);
         exit(1);
     }

Thanks,
Gavin