From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 055881EF39A for ; Tue, 1 Apr 2025 10:12:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743502354; cv=none; b=X7w8FVJSjHgX5xGBKdQNSVyxYCks5VizwYfwLQpiAb+opoTHlaOhhiDcOoqtCpK3QPkikp9AsdtcoUquHzlqU2Q9Gi3CaoCfH36ckWz8S3x0H5FpU7qe4180AzYY6zEl5RfwcrAGlG67ewCEK4SYfgoPMWoUYbXSUZvh8YBaZvc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743502354; c=relaxed/simple; bh=xAL++FE93adr27VON8GPMhrsRR7Iv7WswJqOqriBV4k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=J38TRQ+zrZPhljc+Y7mpdjKB+NdqaMIn2JjvXG4QgGZ411gE3/pJaaiaNKl2Vw5zeWACYFxRLz7AsEfOOfH6X1HdxLw6p3LLiTxoalmXg/LPDcDDIfRhWSCBuFk3bT0hteYWrytEj9w7zKr1TQOrdV2ubLjhBCXWbaRwf/qAc9k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=uq2D60Pq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="uq2D60Pq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1EFCFC4CEE4; Tue, 1 Apr 2025 10:12:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743502353; bh=xAL++FE93adr27VON8GPMhrsRR7Iv7WswJqOqriBV4k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uq2D60Pquq75DNTPmBUzl9Z6jk0WPoeHehqBemxUhzoWGEi06gLXQ9bhsONLjzpqB inffZewEWMlf4GFNfJiGoGjxhdHXW11fKYUI8ZvN9ZDsATUM3CYcef7qWX8KsFnqfL 2mF/hs0YkqJ1Lzvddbt6MtnUg4Hnsf3HIu89tnmYCS/q7jFmgFNGGMOM0PtpCmXX1v RWlfIHRPGUyYlRlJsiJSEYSTTEsGRt6nn1OI7TEIJ9fP2y5815f0naaUTAUoBGMfqv hpoWTYQwQ7WTfB6BFAE8FSJtBiQ+lmFiHIwpGLHM3nX1yJVgC1kPcFGQitiizyI7y4 RsLJuufRUFzTA== Date: Tue, 1 Apr 2025 13:12:25 +0300 From: Mike Rapoport To: Ryan Roberts Cc: Dev Jain , catalin.marinas@arm.com, will@kernel.org, gshan@redhat.com, steven.price@arm.com, suzuki.poulose@arm.com, tianyaxiong@kylinos.cn, ardb@kernel.org, david@redhat.com, urezki@gmail.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: pageattr: Explicitly bail out when changing permissions for vmalloc_huge mappings Message-ID: References: <20250328062103.79462-1-dev.jain@arm.com> <0aac96b5-b3ac-47ee-97af-7ca5d927bdd0@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0aac96b5-b3ac-47ee-97af-7ca5d927bdd0@arm.com> Hi Ryan, On Tue, Apr 01, 2025 at 10:43:01AM +0100, Ryan Roberts wrote: > On 30/03/2025 03:32, Mike Rapoport wrote: > > On Sat, Mar 29, 2025 at 09:46:56AM +0000, Ryan Roberts wrote: > >> On 28/03/2025 18:50, Mike Rapoport wrote: > >>> On Fri, Mar 28, 2025 at 11:51:03AM +0530, Dev Jain wrote: > >>>> arm64 uses apply_to_page_range to change permissions for kernel VA mappings, > >>> > >>> for vmalloc mappings ^ > >>> > >>> arm64 does not allow changing permissions to any VA address right now. > >>> > >>>> which does not support changing permissions for leaf mappings. This function > >>>> will change permissions until it encounters a leaf mapping, and will bail > >>>> out. To avoid this partial change, explicitly disallow changing permissions > >>>> for VM_ALLOW_HUGE_VMAP mappings. > >>>> > >>>> Signed-off-by: Dev Jain > >> > >> I wonder if we want a Fixes: tag here? It's certainly a *latent* bug. > > > > We have only a few places that use vmalloc_huge() or VM_ALLOW_HUGE_VMAP and > > if there was a code that plays permission games on these allocations, x86 > > set_memory would blow up immediately, so I don't think Fixes: is needed > > here. > > Hi Mike, > > I think I may have misunderstood your comments when we spoke at LSF/MM the other > day, as this statement seems to contradict. I thought you said that on x86 BPF > allocates memory using vmalloc_huge()/VM_ALLOW_HUGE_VMAP and then it's > sub-allocator will set_memory_*() on a sub-region of that allocation? (And we > then agreed that it would be good for arm64 to eventually support this with BBML2). I misremembered :) They do allocate several PMD_SIZE chunks at once, but they don't use vmalloc_huge(), so everything there is mapped with base pages. And now they are using execmem rather than vmalloc directly, and execmem doesn't use VM_ALLOW_HUGE_VMAP anywhere except modules on x86. > Anyway, regardless, I think this change is useful first step to improving > vmalloc as it makes us more defensive against any future attempt to change > permissions on a huge allocation. In the long term I'd like to get to the point > where arm64 (with BBML2) can map with VM_ALLOW_HUGE_VMAP by default. > > Thanks, > Ryan -- Sincerely yours, Mike.