Re: [PATCH v3 2/7] arm64/runtime-const: Use aarch64_insn_patch_text_nosync() for patching

From: Catalin Marinas <catalin.marinas@arm.com>
To: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: "Thomas Gleixner" <tglx@kernel.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	"Will Deacon" <will@kernel.org>,
	"David Laight" <david.laight.linux@gmail.com>,
	"Darren Hart" <dvhart@infradead.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"André Almeida" <andrealmeid@igalia.com>,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-s390@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	"Jisheng Zhang" <jszhang@kernel.org>
Subject: Re: [PATCH v3 2/7] arm64/runtime-const: Use aarch64_insn_patch_text_nosync() for patching
Date: Fri, 10 Apr 2026 10:37:45 +0100	[thread overview]
Message-ID: <adjE6WzFM7NogzlU@arm.com> (raw)
In-Reply-To: <20260402112250.2138-3-kprateek.nayak@amd.com>

On Thu, Apr 02, 2026 at 11:22:45AM +0000, K Prateek Nayak wrote:
> diff --git a/arch/arm64/include/asm/runtime-const.h b/arch/arm64/include/asm/runtime-const.h
> index c3dbd3ae68f6..a3106f80912b 100644
> --- a/arch/arm64/include/asm/runtime-const.h
> +++ b/arch/arm64/include/asm/runtime-const.h
> @@ -7,6 +7,7 @@
>  #endif
>  
>  #include <asm/cacheflush.h>
> +#include <asm/text-patching.h>
>  
>  /* Sigh. You can still run arm64 in BE mode */
>  #include <asm/byteorder.h>
> @@ -50,13 +51,7 @@ static inline void __runtime_fixup_16(__le32 *p, unsigned int val)
>  	u32 insn = le32_to_cpu(*p);
>  	insn &= 0xffe0001f;
>  	insn |= (val & 0xffff) << 5;
> -	*p = cpu_to_le32(insn);
> -}
> -
> -static inline void __runtime_fixup_caches(void *where, unsigned int insns)
> -{
> -	unsigned long va = (unsigned long)where;
> -	caches_clean_inval_pou(va, va + 4*insns);
> +	aarch64_insn_patch_text_nosync(p, insn);
>  }

Sashiko has some good points here:

https://sashiko.dev/#/patchset/20260402112250.2138-1-kprateek.nayak@amd.com

In short, aarch64_insn_patch_text_nosync() does not expect a linear map
address but rather a kernel text one (or vmalloc/modules). The other
valid point is on aliasing I-caches.

I think dropping the lm_alias() and just use 'where' directly would do
but I haven't tried.

-- 
Catalin