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)
77 lines
3.1 KiB
Diff
77 lines
3.1 KiB
Diff
From 0aea786f8ab4f7a4122bb2019ebe5136763c9609 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 13:36:39 +0100
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Subject: [PATCH 09/43] include/qemu/compiler: add QEMU_UNINITIALIZED attribute
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macro
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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: [1/31] ddf39e782add4426708480dfb78ebbd71fb777f0 (stefanha/centos-stream-qemu-kvm)
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The QEMU_UNINITIALIZED macro is to be used to skip the default compiler
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variable initialization done by -ftrivial-auto-var-init=zero.
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Use this in cases where there a method in the device I/O path (or other
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important hot paths), that has large variables on the stack. A rule of
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thumb is that "large" means a method with 4kb data in the local stack
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frame. Any variables which are KB in size, should be annotated with this
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attribute, to pre-emptively eliminate any potential overhead from the
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compiler zero'ing memory.
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Given that this turns off a security hardening feature, when using this
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to flag variables, it is important that the code is double-checked to
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ensure there is no possible use of uninitialized data in the method.
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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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Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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Message-id: 20250610123709.835102-2-berrange@redhat.com
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[DB: split off patch & rewrite guidance on when to use the annotation]
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Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit c653b67d1863b7ebfa67f7c9f4aec209d7b5ced5)
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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---
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include/qemu/compiler.h | 20 ++++++++++++++++++++
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1 file changed, 20 insertions(+)
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diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
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index 496dac5ac1..65b89958d3 100644
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--- a/include/qemu/compiler.h
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+++ b/include/qemu/compiler.h
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@@ -207,6 +207,26 @@
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# define QEMU_USED
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#endif
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+/*
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+ * Disable -ftrivial-auto-var-init on a local variable.
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+ *
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+ * Use this in cases where there a method in the device I/O path (or other
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+ * important hot paths), that has large variables on the stack. A rule of
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+ * thumb is that "large" means a method with 4kb data in the local stack
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+ * frame. Any variables which are KB in size, should be annotated with this
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+ * attribute, to pre-emptively eliminate any potential overhead from the
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+ * compiler's implicit zero'ing of memory.
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+ *
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+ * Given that this turns off a security hardening feature, when using this
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+ * to flag variables, it is important that the code is double-checked to
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+ * ensure there is no possible use of uninitialized data in the method.
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+ */
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+#if __has_attribute(uninitialized)
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+# define QEMU_UNINITIALIZED __attribute__((uninitialized))
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+#else
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+# define QEMU_UNINITIALIZED
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+#endif
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+
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/*
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* http://clang.llvm.org/docs/ThreadSafetyAnalysis.html
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*
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--
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2.39.3
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