58099777f4
Fix by replacing memset with manual 0 assignments. The first patch was rightly rejected by upstream as it affects everything so keep it in 9xx. Upstream message for it is: dcbz instruction shouldn't be used on non-cached memory. Using it on non-cached memory can result in alignment exception and implies a heavy handling. Instead of silentely emulating the instruction and resulting in high performance degradation, warn whenever an alignment exception is taken in kernel mode due to dcbz, so that the user is made aware that dcbz instruction has been used unexpectedly by the kernel. Signed-off-by: Rosen Penev <rosenp@gmail.com> Link: https://github.com/openwrt/openwrt/pull/23382 Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
73 lines
2.2 KiB
Diff
73 lines
2.2 KiB
Diff
From 78bddfc01439de243624b1e60a7f599ec11b55b7 Mon Sep 17 00:00:00 2001
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From: Rosen Penev <rosenp@gmail.com>
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Date: Sat, 16 May 2026 16:08:49 -0700
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Subject: [PATCH] dma-direct: Clear pages before coherent remap
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Clear pages through their page mapping before creating a coherent
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remap for dma-direct allocations. Some architectures implement the
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coherent remap as uncached memory, where the generic memset() path may
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use cache-only zeroing instructions that are not valid for the returned
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CPU mapping.
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Keep the existing memset() for non-remapped allocations, but avoid
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normal memset() on the remapped coherent allocation path.
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Assisted-by: Codex:GPT-5.5
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Signed-off-by: Rosen Penev <rosenp@gmail.com>
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---
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kernel/dma/direct.c | 20 ++++++++++++++++++--
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1 file changed, 18 insertions(+), 2 deletions(-)
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--- a/kernel/dma/direct.c
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+++ b/kernel/dma/direct.c
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@@ -8,6 +8,7 @@
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#include <linux/export.h>
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#include <linux/mm.h>
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#include <linux/dma-map-ops.h>
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+#include <linux/highmem.h>
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#include <linux/scatterlist.h>
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#include <linux/pfn.h>
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#include <linux/vmalloc.h>
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@@ -104,6 +105,15 @@ static void __dma_direct_free_pages(stru
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dma_free_contiguous(dev, page, size);
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}
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+static void dma_direct_zero_pages(struct page *page, size_t size)
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+{
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+ unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
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+ unsigned long i;
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+
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+ for (i = 0; i < count; i++)
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+ clear_highpage(page + i);
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+}
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+
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static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t size)
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{
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struct page *page = swiotlb_alloc(dev, size);
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@@ -268,6 +278,13 @@ void *dma_direct_alloc(struct device *de
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if (remap) {
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pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
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+ /*
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+ * Zero via the page mapping before creating a potentially
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+ * uncached remap. Some architectures cannot safely run normal
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+ * memset on uncached memory.
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+ */
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+ dma_direct_zero_pages(page, size);
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+
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if (force_dma_unencrypted(dev))
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prot = pgprot_decrypted(prot);
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@@ -283,10 +300,9 @@ void *dma_direct_alloc(struct device *de
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ret = page_address(page);
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if (dma_set_decrypted(dev, ret, size))
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goto out_leak_pages;
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+ memset(ret, 0, size);
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}
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- memset(ret, 0, size);
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-
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if (set_uncached) {
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arch_dma_prep_coherent(page, size);
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ret = arch_dma_set_uncached(ret, size);
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