qemu-kvm/SOURCES/kvm-memory-device-reintroduce-memory-region-size-check.patch

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From 633c6a52ac88526534466ae311522fe5447bcf91 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@redhat.com>
Date: Wed, 17 Jan 2024 14:55:54 +0100
Subject: [PATCH 02/22] memory-device: reintroduce memory region size check
RH-Author: David Hildenbrand <david@redhat.com>
RH-MergeRequest: 221: memory-device: reintroduce memory region size check
RH-Jira: RHEL-20341
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Acked-by: Igor Mammedov <imammedo@redhat.com>
RH-Commit: [2/2] e9ff2339b0c07c3f48f5834c9c80cd6d4cbc8f71
JIRA: https://issues.redhat.com/browse/RHEL-20341
We used to check that the memory region size is multiples of the overall
requested address alignment for the device memory address.
We removed that check, because there are cases (i.e., hv-balloon) where
devices unconditionally request an address alignment that has a very large
alignment (i.e., 32 GiB), but the actual memory device size might not be
multiples of that alignment.
However, this change:
(a) allows for some practically impossible DIMM sizes, like "1GB+1 byte".
(b) allows for DIMMs that partially cover hugetlb pages, previously
reported in [1].
Both scenarios don't make any sense: we might even waste memory.
So let's reintroduce that check, but only check that the
memory region size is multiples of the memory region alignment (i.e.,
page size, huge page size), but not any additional memory device
requirements communicated using md->get_min_alignment().
The following examples now fail again as expected:
(a) 1M with 2M THP
qemu-system-x86_64 -m 4g,maxmem=16g,slots=1 -S -nodefaults -nographic \
-object memory-backend-ram,id=mem1,size=1M \
-device pc-dimm,id=dimm1,memdev=mem1
-> backend memory size must be multiple of 0x200000
(b) 1G+1byte
qemu-system-x86_64 -m 4g,maxmem=16g,slots=1 -S -nodefaults -nographic \
-object memory-backend-ram,id=mem1,size=1073741825B \
-device pc-dimm,id=dimm1,memdev=mem1
-> backend memory size must be multiple of 0x200000
(c) Unliagned hugetlb size (2M)
qemu-system-x86_64 -m 4g,maxmem=16g,slots=1 -S -nodefaults -nographic \
-object memory-backend-file,id=mem1,mem-path=/dev/hugepages/tmp,size=511M \
-device pc-dimm,id=dimm1,memdev=mem1
backend memory size must be multiple of 0x200000
(d) Unliagned hugetlb size (1G)
qemu-system-x86_64 -m 4g,maxmem=16g,slots=1 -S -nodefaults -nographic \
-object memory-backend-file,id=mem1,mem-path=/dev/hugepages1G/tmp,size=2047M \
-device pc-dimm,id=dimm1,memdev=mem1
-> backend memory size must be multiple of 0x40000000
Note that this fix depends on a hv-balloon change to communicate its
additional alignment requirements using get_min_alignment() instead of
through the memory region.
[1] https://lkml.kernel.org/r/f77d641d500324525ac036fe1827b3070de75fc1.1701088320.git.mprivozn@redhat.com
Message-ID: <20240117135554.787344-3-david@redhat.com>
Reported-by: Zhenyu Zhang <zhenyzha@redhat.com>
Reported-by: Michal Privoznik <mprivozn@redhat.com>
Fixes: eb1b7c4bd413 ("memory-device: Drop size alignment check")
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
(cherry picked from commit 540a1abbf0b243e4cfb4333c5d30a041f7080ba4)
Signed-off-by: David Hildenbrand <david@redhat.com>
---
hw/mem/memory-device.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/hw/mem/memory-device.c b/hw/mem/memory-device.c
index a1b1af26bc..e098585cda 100644
--- a/hw/mem/memory-device.c
+++ b/hw/mem/memory-device.c
@@ -374,6 +374,20 @@ void memory_device_pre_plug(MemoryDeviceState *md, MachineState *ms,
goto out;
}
+ /*
+ * We always want the memory region size to be multiples of the memory
+ * region alignment: for example, DIMMs with 1G+1byte size don't make
+ * any sense. Note that we don't check that the size is multiples
+ * of any additional alignment requirements the memory device might
+ * have when it comes to the address in physical address space.
+ */
+ if (!QEMU_IS_ALIGNED(memory_region_size(mr),
+ memory_region_get_alignment(mr))) {
+ error_setg(errp, "backend memory size must be multiple of 0x%"
+ PRIx64, memory_region_get_alignment(mr));
+ return;
+ }
+
if (legacy_align) {
align = *legacy_align;
} else {
--
2.39.3