From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (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 17C583A425B for ; Tue, 4 Aug 2026 10:12:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785838369; cv=none; b=bSOqxMdu+eHWRMa1JjeM9dFIZ8i7MToeG+l7pjyU6mXUREP6060ljzv3zTnZ9bOGTYphkfXe2hsrILrmQoexwAq7OPwQV8jp2e4Q7x9KR6u5yw4Z7Vlgi/EyEv29nvsQJ041SAkW/C/HdxWmRK3U4l3rAulz3X3eltVzPx7nf64= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785838369; c=relaxed/simple; bh=g+bCO5vxx/6RBIiB9FA7NYcSOsBWCY2kMQJH1Z0HiZA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NvT7F/fhUsqMgX2UeT+FoeOgnZlmmr9/WYQY1rGfJqYN5h0ZxMlvEK+H4HfRJUdbAOT0C8xJs82UtbgppvPSLwaFdJxzwvqcf8Xug1oYeHmt8hsN5iuACH1v6nu6RnAhBU/XJb1dp+nd/MupR3eat868xEUfyRu5b2ZdVSVEUGE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=blTeJldW; arc=none smtp.client-ip=95.215.58.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="blTeJldW" Date: Tue, 4 Aug 2026 12:12:33 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785838362; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1t/mDVvfxOYXQFVZOi5AcTPB8k6kOMpFsEIx8w8UP7c=; b=blTeJldWikI9rBHH9TbiR6hP7r+osk2v37MigEmWWQGcfDfleyMUhTmfxlIvkkSwlUTp20 TEZjdSdqbkmvcRKPbmnLCvK0FgqgK3PwoMHk/2fhtD04KxxhoxvWaQisray27Uu6rr38/2 PRiJFCPmdeKwJdTuiKEy/w02MW2anto= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Thorsten Blum To: Ingo Molnar Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND] x86/fpu: Use vmemdup_user() in xstateregs_set() Message-ID: References: <20260720195534.70111-3-thorsten.blum@linux.dev> 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: X-Migadu-Flow: FLOW_OUT On Sun, Aug 02, 2026 at 03:20:59PM +0200, Ingo Molnar wrote: > * Thorsten Blum wrote: > > > Replace the open-coded vmalloc() and copy_from_user() with > > > vmemdup_user() to simplify xstateregs_set(). > > > > > > vmemdup_user() returns an ERR_PTR() on failure, preserving the existing > > > -ENOMEM and -EFAULT error codes. Since vmemdup_user() is backed by > > > kvmalloc(), use kvfree() to free the buffer instead. > > > > > > Return early on error and drop the obsolete out label. > > > I've resent this cleanup a few times and haven't received feedback. Is > > this still something you would consider, or would you prefer that I drop > > it? It's intended to be a mechanical cleanup with no functional changes. > > > > Happy to rerun the relevant x86 XSAVE selftests if it helps. > > So the changelog is silent on any potential side-effects of this change. > vmalloc will return page-aligned addresses. kmalloc won't. Will this > have any effects on performance? > > Are there other examples of vmalloc() -> kvmalloc() conversions in > the tree, is it a recommended and well-tested technique to simplify > the code? > > A very quick git log investigation does not seem to be showing > any such recent conversion examples: > > starship:~/tip> git log -E --grep='kvmalloc' --since=one-year-ago | grep -w vmalloc > > I'm not opposed to it in principle, I just think the 'analysis' > side of the patch description is basically non-existent. Performance should be similar, and it's not a hot path. Page alignment shouldn't matter because the buffer is only used as a memcpy() source in copy_uabi_from_kernel_to_xstate(). The main difference is that vmemdup_user() uses GFP_USER, which adds __GFP_HARDWALL and may change cpuset allocations. The avx_64 selftests also pass on my Alder Lake CPU: [RUN] AVX registers: check context switches, 10 iterations, 5 threads. [OK] No incorrect case was found. [RUN] AVX registers: inject xstate via ptrace(). [OK] 'xfeatures' in SW reserved area was correctly written [OK] xstate was correctly updated. [RUN] AVX registers: load xstate and raise SIGUSR1 [OK] 'magic1' is valid [OK] 'xfeatures' in SW reserved area is valid [OK] 'xfeatures' in XSAVE header is valid [OK] xstate delivery was successful [OK] 'magic2' is valid [RUN] AVX registers: load new xstate from sighandler and check it after sigreturn [OK] xstate was restored correctly # The kernel does not support feature number: 5 # The kernel does not support feature number: 6 # The kernel does not support feature number: 7 Thanks, Thorsten