add392f0f0
- kvm-meson-configure-add-valgrind-option-en-dis-able-valg.patch [RHEL-88153] - kvm-distro-add-an-explicit-valgrind-devel-build-dep.patch [RHEL-88153] - kvm-hw-i386-Fix-machine-type-compatibility.patch [RHEL-91307] - kvm-vfio-helpers-Refactor-vfio_region_mmap-error-handlin.patch [RHEL-88533] - kvm-vfio-helpers-Align-mmaps.patch [RHEL-88533] - Resolves: RHEL-88153 ([s390x] valgrind not working with qemu-kvm for non-x86 builds) - Resolves: RHEL-91307 (Fix x86 M-type compats) - Resolves: RHEL-88533 (Improve VFIO mmapping performance with huge pfnmaps)
101 lines
4.3 KiB
Diff
101 lines
4.3 KiB
Diff
From 0e733c43122688a40b0bad9cf9af43ac3655fa30 Mon Sep 17 00:00:00 2001
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From: Alex Williamson <alex.williamson@redhat.com>
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Date: Tue, 22 Oct 2024 14:08:29 -0600
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Subject: [PATCH 5/5] vfio/helpers: Align mmaps
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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: Donald Dutile <None>
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RH-MergeRequest: 366: Improve VFIO mmapping performance with huge pfnmaps
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RH-Jira: RHEL-88533
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RH-Acked-by: Cédric Le Goater <clg@redhat.com>
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RH-Acked-by: Alex Williamson <None>
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RH-Commit: [2/2] f0e99cf993f82796352376bc7280342729ea5624 (ddutile/qemu-kvm)
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Thanks to work by Peter Xu, support is introduced in Linux v6.12 to
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allow pfnmap insertions at PMD and PUD levels of the page table. This
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means that provided a properly aligned mmap, the vfio driver is able
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to map MMIO at significantly larger intervals than PAGE_SIZE. For
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example on x86_64 (the only architecture currently supporting huge
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pfnmaps for PUD), rather than 4KiB mappings, we can map device MMIO
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using 2MiB and even 1GiB page table entries.
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Typically mmap will already provide PMD aligned mappings, so devices
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with moderately sized MMIO ranges, even GPUs with standard 256MiB BARs,
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will already take advantage of this support. However in order to better
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support devices exposing multi-GiB MMIO, such as 3D accelerators or GPUs
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with resizable BARs enabled, we need to manually align the mmap.
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There doesn't seem to be a way for userspace to easily learn about PMD
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and PUD mapping level sizes, therefore this takes the simple approach
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to align the mapping to the power-of-two size of the region, up to 1GiB,
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which is currently the maximum alignment we care about.
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Cc: Peter Xu <peterx@redhat.com>
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Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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Reviewed-by: Peter Xu <peterx@redhat.com>
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Reviewed-by: Cédric Le Goater <clg@redhat.com>
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(cherry picked from commit 00b519c0bca0e933ed22e2e6f8bca6b23f41f950)
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Jira: https://issues.redhat.com/browse/RHEL-88533
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Signed-off-by: Donald Dutile <ddutile@redhat.com>
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---
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hw/vfio/helpers.c | 32 ++++++++++++++++++++++++++++++--
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1 file changed, 30 insertions(+), 2 deletions(-)
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diff --git a/hw/vfio/helpers.c b/hw/vfio/helpers.c
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index b9e606e364..913796f437 100644
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--- a/hw/vfio/helpers.c
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+++ b/hw/vfio/helpers.c
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@@ -27,6 +27,7 @@
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#include "trace.h"
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#include "qapi/error.h"
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#include "qemu/error-report.h"
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+#include "qemu/units.h"
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#include "monitor/monitor.h"
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/*
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@@ -406,8 +407,35 @@ int vfio_region_mmap(VFIORegion *region)
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prot |= region->flags & VFIO_REGION_INFO_FLAG_WRITE ? PROT_WRITE : 0;
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for (i = 0; i < region->nr_mmaps; i++) {
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- region->mmaps[i].mmap = mmap(NULL, region->mmaps[i].size, prot,
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- MAP_SHARED, region->vbasedev->fd,
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+ size_t align = MIN(1ULL << ctz64(region->mmaps[i].size), 1 * GiB);
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+ void *map_base, *map_align;
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+
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+ /*
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+ * Align the mmap for more efficient mapping in the kernel. Ideally
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+ * we'd know the PMD and PUD mapping sizes to use as discrete alignment
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+ * intervals, but we don't. As of Linux v6.12, the largest PUD size
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+ * supporting huge pfnmap is 1GiB (ARCH_SUPPORTS_PUD_PFNMAP is only set
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+ * on x86_64). Align by power-of-two size, capped at 1GiB.
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+ *
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+ * NB. qemu_memalign() and friends actually allocate memory, whereas
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+ * the region size here can exceed host memory, therefore we manually
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+ * create an oversized anonymous mapping and clean it up for alignment.
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+ */
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+ map_base = mmap(0, region->mmaps[i].size + align, PROT_NONE,
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+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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+ if (map_base == MAP_FAILED) {
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+ ret = -errno;
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+ goto no_mmap;
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+ }
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+
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+ map_align = (void *)ROUND_UP((uintptr_t)map_base, (uintptr_t)align);
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+ munmap(map_base, map_align - map_base);
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+ munmap(map_align + region->mmaps[i].size,
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+ align - (map_align - map_base));
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+
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+ region->mmaps[i].mmap = mmap(map_align, region->mmaps[i].size, prot,
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+ MAP_SHARED | MAP_FIXED,
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+ region->vbasedev->fd,
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region->fd_offset +
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region->mmaps[i].offset);
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if (region->mmaps[i].mmap == MAP_FAILED) {
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--
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2.48.1
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