kernel_5.10 no rt

hc

2023-12-11 6778948f9de86c3cfaf36725a7c87dcff9ba247f

 kernel/arch/x86/kernel/crash_dump_32.c
..
..
@@ -13,6 +13,8 @@
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 #include <linux/uaccess.h>
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+static void *kdump_buf_page;
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+
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 static inline bool is_crashed_pfn_valid(unsigned long pfn)
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 {
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 #ifndef CONFIG_X86_PAE
..
..
@@ -39,11 +41,15 @@
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  * @userbuf: if set, @buf is in user address space, use copy_to_user(),
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  *	otherwise @buf is in kernel address space, use memcpy().
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  *
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- * Copy a page from "oldmem". For this page, there might be no pte mapped
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- * in the current kernel.
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+ * Copy a page from "oldmem". For this page, there is no pte mapped
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+ * in the current kernel. We stitch up a pte, similar to kmap_atomic.
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+ *
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+ * Calling copy_to_user() in atomic context is not desirable. Hence first
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+ * copying the data to a pre-allocated kernel page and then copying to user
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+ * space in non-atomic context.
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  */
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-ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
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-			 unsigned long offset, int userbuf)
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+ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
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+                               size_t csize, unsigned long offset, int userbuf)
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 {
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 	void  *vaddr;
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..
..
@@ -53,16 +59,38 @@
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 	if (!is_crashed_pfn_valid(pfn))
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 		return -EFAULT;
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-	vaddr = kmap_local_pfn(pfn);
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+	vaddr = kmap_atomic_pfn(pfn);
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 	if (!userbuf) {
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-		memcpy(buf, vaddr + offset, csize);
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+		memcpy(buf, (vaddr + offset), csize);
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+		kunmap_atomic(vaddr);
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 	} else {
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-		if (copy_to_user(buf, vaddr + offset, csize))
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-			csize = -EFAULT;
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+		if (!kdump_buf_page) {
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+			printk(KERN_WARNING "Kdump: Kdump buffer page not"
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+				" allocated\n");
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+			kunmap_atomic(vaddr);
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+			return -EFAULT;
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+		}
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+		copy_page(kdump_buf_page, vaddr);
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+		kunmap_atomic(vaddr);
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+		if (copy_to_user(buf, (kdump_buf_page + offset), csize))
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+			return -EFAULT;
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 	}
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-
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-	kunmap_local(vaddr);
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 	return csize;
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 }
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+
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+static int __init kdump_buf_page_init(void)
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+{
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+	int ret = 0;
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+
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+	kdump_buf_page = kmalloc(PAGE_SIZE, GFP_KERNEL);
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+	if (!kdump_buf_page) {
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+		printk(KERN_WARNING "Kdump: Failed to allocate kdump buffer"
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+			 " page\n");
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+		ret = -ENOMEM;
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+	}
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+
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+	return ret;
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+}
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+arch_initcall(kdump_buf_page_init);