On Fri, Jul 24, 2020 at 01:13:02PM +0300, Mike Rapoport wrote:

On Fri, Jul 24, 2020 at 01:28:35AM +0300, Jarkko Sakkinen wrote:

quoted

On Sat, Jul 18, 2020 at 07:23:59PM +0300, Mike Rapoport wrote:

quoted

On Fri, Jul 17, 2020 at 06:04:17AM +0300, Jarkko Sakkinen wrote:

quoted

Introduce functions for allocating memory for dynamic trampolines, such
as kprobes. An arch can promote the availability of these functions with
CONFIG_ARCH_HAS_TEXT_ALLOC. Provide default/fallback implementation
wrapping module_alloc() and module_memfree().

Cc: Andi Kleen <redacted>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jarkko Sakkinen <redacted>
---
 include/linux/vmalloc.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 0221f852a7e1..e981436e30b6 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h

@@ -9,6 +9,7 @@
 #include <asm/page.h>		/* pgprot_t */
 #include <linux/rbtree.h>
 #include <linux/overflow.h>
+#include <linux/moduleloader.h>
 
 #include <asm/vmalloc.h>
 

@@ -249,4 +250,26 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
 int register_vmap_purge_notifier(struct notifier_block *nb);
 int unregister_vmap_purge_notifier(struct notifier_block *nb);
 
+#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC
+/*
+ * Allocate memory to be used for dynamic trampoline code.
+ */
+void *text_alloc(unsigned long size);
+
+/*
+ * Free memory returned from text_alloc().
+ */
+void text_free(void *region);
+#else
+static inline void *text_alloc(unsigned long size)
+{
+	return module_alloc(size);
+}
+
+static inline void text_free(void *region)
+{
+	module_memfree(region);
+}

Using module_alloc() as the default implementation of generic
text_alloc() does not sound right to me.

I would suggest rename module_alloc() to text_alloc() on x86, as Peter
proposed and then add text_alloc_kprobes() that can be overridden by the
architectures. x86 could use text_alloc(), arm64 vmalloc() with options
of their choice and the fallback would remain module_alloc(). Something
like (untested) patch below:

I'm not exactly sure which of the below is relevant as the patch set
includes the exact same changes with maybe different phrasing:

The difference in parsing is what differentiates semantically clean code
from duct tape.

As several people pointed out, a single text_alloc(), and apprently a
single ARCH_HAS_TEXT_ALLOC, would not fit all architectures and some
ground work required to implement a generic text allocation.

Your patch works aroung this for x86 with broken semantics of
text_alloc() when ARCH_HAS_TEXT_ALLOC is not defined.

My suggestion does not make text_alloc() a special case of
module_alloc() but rather makes text_alloc_kprobes() to fallback to
module_alloc() when architecture does not provide its implementation.

OK, I see your point now. I'll response in detail to v5 comments.

Thank you.

/Jarkko