0dde13a5cd
- kvm-s390x-Fix-leak-in-machine_set_loadparm.patch [RHEL-98555] - kvm-hw-s390x-ccw-device-Fix-memory-leak-in-loadparm-sett.patch [RHEL-98555] - kvm-target-i386-Update-EPYC-CPU-model-for-Cache-property.patch [RHEL-52650] - kvm-target-i386-Update-EPYC-Rome-CPU-model-for-Cache-pro.patch [RHEL-52650] - kvm-target-i386-Update-EPYC-Milan-CPU-model-for-Cache-pr.patch [RHEL-52650] - kvm-target-i386-Add-couple-of-feature-bits-in-CPUID_Fn80.patch [RHEL-52650] - kvm-target-i386-Update-EPYC-Genoa-for-Cache-property-per.patch [RHEL-52650] - kvm-target-i386-Add-support-for-EPYC-Turin-model.patch [RHEL-52650] - kvm-include-qemu-compiler-add-QEMU_UNINITIALIZED-attribu.patch [RHEL-95479] - kvm-hw-virtio-virtio-avoid-cost-of-ftrivial-auto-var-ini.patch [RHEL-95479] - kvm-block-skip-automatic-zero-init-of-large-array-in-ioq.patch [RHEL-95479] - kvm-chardev-char-fd-skip-automatic-zero-init-of-large-ar.patch [RHEL-95479] - kvm-chardev-char-pty-skip-automatic-zero-init-of-large-a.patch [RHEL-95479] - kvm-chardev-char-socket-skip-automatic-zero-init-of-larg.patch [RHEL-95479] - kvm-hw-audio-ac97-skip-automatic-zero-init-of-large-arra.patch [RHEL-95479] - kvm-hw-audio-cs4231a-skip-automatic-zero-init-of-large-a.patch [RHEL-95479] - kvm-hw-audio-es1370-skip-automatic-zero-init-of-large-ar.patch [RHEL-95479] - kvm-hw-audio-gus-skip-automatic-zero-init-of-large-array.patch [RHEL-95479] - kvm-hw-audio-marvell_88w8618-skip-automatic-zero-init-of.patch [RHEL-95479] - kvm-hw-audio-sb16-skip-automatic-zero-init-of-large-arra.patch [RHEL-95479] - kvm-hw-audio-via-ac97-skip-automatic-zero-init-of-large-.patch [RHEL-95479] - kvm-hw-char-sclpconsole-lm-skip-automatic-zero-init-of-l.patch [RHEL-95479] - kvm-hw-dma-xlnx_csu_dma-skip-automatic-zero-init-of-larg.patch [RHEL-95479] - kvm-hw-display-vmware_vga-skip-automatic-zero-init-of-la.patch [RHEL-95479] - kvm-hw-hyperv-syndbg-skip-automatic-zero-init-of-large-a.patch [RHEL-95479] - kvm-hw-misc-aspeed_hace-skip-automatic-zero-init-of-larg.patch [RHEL-95479] - kvm-hw-net-rtl8139-skip-automatic-zero-init-of-large-arr.patch [RHEL-95479] - kvm-hw-net-tulip-skip-automatic-zero-init-of-large-array.patch [RHEL-95479] - kvm-hw-net-virtio-net-skip-automatic-zero-init-of-large-.patch [RHEL-95479] - kvm-hw-net-xgamc-skip-automatic-zero-init-of-large-array.patch [RHEL-95479] - kvm-hw-nvme-ctrl-skip-automatic-zero-init-of-large-array.patch [RHEL-95479] - kvm-hw-ppc-pnv_occ-skip-automatic-zero-init-of-large-str.patch [RHEL-95479] - kvm-hw-ppc-spapr_tpm_proxy-skip-automatic-zero-init-of-l.patch [RHEL-95479] - kvm-hw-usb-hcd-ohci-skip-automatic-zero-init-of-large-ar.patch [RHEL-95479] - kvm-hw-scsi-lsi53c895a-skip-automatic-zero-init-of-large.patch [RHEL-95479] - kvm-hw-scsi-megasas-skip-automatic-zero-init-of-large-ar.patch [RHEL-95479] - kvm-hw-ufs-lu-skip-automatic-zero-init-of-large-array.patch [RHEL-95479] - kvm-net-socket-skip-automatic-zero-init-of-large-array.patch [RHEL-95479] - kvm-net-stream-skip-automatic-zero-init-of-large-array.patch [RHEL-95479] - kvm-hw-i386-amd_iommu-Isolate-AMDVI-PCI-from-amd-iommu-d.patch [RHEL-85649] - kvm-hw-i386-amd_iommu-Allow-migration-when-explicitly-cr.patch [RHEL-85649] - kvm-Enable-amd-iommu-device.patch [RHEL-85649] - kvm-ui-vnc-Update-display-update-interval-when-VM-state-.patch [RHEL-83883] - Resolves: RHEL-98555 ([s390x][RHEL10.1][ccw-device] there would be memory leak with virtio_blk disks) - Resolves: RHEL-52650 ([AMDSERVER 10.1 Feature] Turin: Qemu EPYC-Turin Model) - Resolves: RHEL-95479 (-ftrivial-auto-var-init=zero reduced performance) - Resolves: RHEL-85649 ([RHEL 10]Qemu/amd-iommu: Add ability to manually specify the AMDVI-PCI device) - Resolves: RHEL-83883 (Video stuck after switchover phase when play one video during migration)
74 lines
3.0 KiB
Diff
74 lines
3.0 KiB
Diff
From 6063d3fedb2767f1a4d668828f49ef8505fa54f3 Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Tue, 10 Jun 2025 13:36:40 +0100
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Subject: [PATCH 10/43] hw/virtio/virtio: avoid cost of -ftrivial-auto-var-init
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in hot path
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
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RH-MergeRequest: 381: Solve -ftrivial-auto-var-init performance regression with QEMU_UNINITIALIZED
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RH-Jira: RHEL-95479
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Commit: [2/31] 12f251ba363203812e46f268a6f46ccfdbf21b41 (stefanha/centos-stream-qemu-kvm)
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Since commit 7ff9ff039380 ("meson: mitigate against use of uninitialize
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stack for exploits") the -ftrivial-auto-var-init=zero compiler option is
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used to zero local variables. While this reduces security risks
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associated with uninitialized stack data, it introduced a measurable
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bottleneck in the virtqueue_split_pop() and virtqueue_packed_pop()
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functions.
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These virtqueue functions are in the hot path. They are called for each
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element (request) that is popped from a VIRTIO device's virtqueue. Using
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__attribute__((uninitialized)) on large stack variables in these
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functions improves fio randread bs=4k iodepth=64 performance from 304k
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to 332k IOPS (+9%).
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This issue was found using perf-top(1). virtqueue_split_pop() was one of
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the top CPU consumers and the "annotate" feature showed that the memory
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zeroing instructions at the beginning of the functions were hot.
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Fixes: 7ff9ff039380 ("meson: mitigate against use of uninitialize stack for exploits")
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Cc: Daniel P. Berrangé <berrange@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Message-id: 20250610123709.835102-3-berrange@redhat.com
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit ba2868ce091cd4abe4be6de4b7e44b3be303b352)
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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---
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hw/virtio/virtio.c | 8 ++++----
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1 file changed, 4 insertions(+), 4 deletions(-)
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diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
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index 85110bce37..f41a418da3 100644
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--- a/hw/virtio/virtio.c
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+++ b/hw/virtio/virtio.c
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@@ -1680,8 +1680,8 @@ static void *virtqueue_split_pop(VirtQueue *vq, size_t sz)
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VirtIODevice *vdev = vq->vdev;
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VirtQueueElement *elem = NULL;
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unsigned out_num, in_num, elem_entries;
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- hwaddr addr[VIRTQUEUE_MAX_SIZE];
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- struct iovec iov[VIRTQUEUE_MAX_SIZE];
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+ hwaddr QEMU_UNINITIALIZED addr[VIRTQUEUE_MAX_SIZE];
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+ struct iovec QEMU_UNINITIALIZED iov[VIRTQUEUE_MAX_SIZE];
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VRingDesc desc;
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int rc;
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@@ -1826,8 +1826,8 @@ static void *virtqueue_packed_pop(VirtQueue *vq, size_t sz)
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VirtIODevice *vdev = vq->vdev;
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VirtQueueElement *elem = NULL;
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unsigned out_num, in_num, elem_entries;
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- hwaddr addr[VIRTQUEUE_MAX_SIZE];
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- struct iovec iov[VIRTQUEUE_MAX_SIZE];
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+ hwaddr QEMU_UNINITIALIZED addr[VIRTQUEUE_MAX_SIZE];
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+ struct iovec QEMU_UNINITIALIZED iov[VIRTQUEUE_MAX_SIZE];
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VRingPackedDesc desc;
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uint16_t id;
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int rc;
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--
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2.39.3
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