From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.7]) (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 C197821A1C for ; Fri, 13 Oct 2023 17:27:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="jwAfOZcw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1697218061; x=1728754061; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=Z8lvOyf3FPZKYPZj2QqKGqflyB0nXwS/NQ0CX5nE1hA=; b=jwAfOZcwTLrTPH3qF3fJ6hyARyffG/QB5/+bPtEyB5zMjOD4xXXxCnB9 RtYK5ybm1xj9CJkMaEPs7ddbLx+gNUM9n2IAjCdT4EpdQVt9I8UnNVXBT JAbAyOqFGlIGB0c2rmzYeiFSIAwcXK2Wey7RnA+ysi2szdPzl1TmveaED i54nNuMLmseQ2hMvWVpuybhIckTO2/joHGewQ7aX7Oni3ak0/DHFTMRnC mMnUnxpYfqv5PTEnByJDanwnB6X0KCtyiD4V2MMqjh96NDV9J3Uca/ItN UNKrOXd/tbwTRiuT0m3FZ933gBYSOeerjzHhqidir929+FzoqCMK5isw+ g==; X-IronPort-AV: E=McAfee;i="6600,9927,10862"; a="6791209" X-IronPort-AV: E=Sophos;i="6.03,222,1694761200"; d="scan'208";a="6791209" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Oct 2023 10:27:39 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10862"; a="878603514" X-IronPort-AV: E=Sophos;i="6.03,222,1694761200"; d="scan'208";a="878603514" Received: from bgras-mobl1.ger.corp.intel.com (HELO box.shutemov.name) ([10.252.59.145]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Oct 2023 10:27:31 -0700 Received: by box.shutemov.name (Postfix, from userid 1000) id 10FE2104A05; Fri, 13 Oct 2023 20:27:28 +0300 (+03) Date: Fri, 13 Oct 2023 20:27:28 +0300 From: "Kirill A. Shutemov" To: Vlastimil Babka Cc: Michael Roth , Borislav Petkov , Andy Lutomirski , Dave Hansen , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel , Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Dario Faggioli , Mike Rapoport , David Hildenbrand , Mel Gorman , marcelo.cerri@canonical.com, tim.gardner@canonical.com, khalid.elmously@canonical.com, philip.cox@canonical.com, aarcange@redhat.com, peterx@redhat.com, x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv14 5/9] efi: Add unaccepted memory support Message-ID: <20231013172728.66pm7os3fp7laxwr@box> References: <20230606142637.5171-1-kirill.shutemov@linux.intel.com> <20230606142637.5171-6-kirill.shutemov@linux.intel.com> <20231010210518.jguawj7bscwgvszv@amd.com> <20231013123358.y4pcdp5fgtt4ax6g@box.shutemov.name> <20231013162210.bqepgz6wnh7uohqq@box> <34d94c58-f5f3-48eb-5833-0ef0c90cf868@suse.cz> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <34d94c58-f5f3-48eb-5833-0ef0c90cf868@suse.cz> On Fri, Oct 13, 2023 at 06:44:45PM +0200, Vlastimil Babka wrote: > On 10/13/23 18:22, Kirill A. Shutemov wrote: > > On Fri, Oct 13, 2023 at 03:33:58PM +0300, Kirill A. Shutemov wrote: > >> > While testing SNP guests running today's tip/master (ef19bc9dddc3) I ran > >> > into what seems to be fairly significant lock contention due to the > >> > unaccepted_memory_lock spinlock above, which results in a constant stream > >> > of soft-lockups until the workload gets all its memory accepted/faulted > >> > in if the guest has around 16+ vCPUs. > >> > > >> > I've included the guest dmesg traces I was seeing below. > >> > > >> > In this case I was running a 32 vCPU guest with 200GB of memory running on > >> > a 256 thread EPYC (Milan) system, and can trigger the above situation fairly > >> > reliably by running the following workload in a freshly-booted guests: > >> > > >> > stress --vm 32 --vm-bytes 5G --vm-keep > >> > > >> > Scaling up the number of stress threads and vCPUs should make it easier > >> > to reproduce. > >> > > >> > Other than unresponsiveness/lockup messages until the memory is accepted, > >> > the guest seems to continue running fine, but for large guests where > >> > unaccepted memory is more likely to be useful, it seems like it could be > >> > an issue, especially when consider 100+ vCPU guests. > >> > >> Okay, sorry for delay. It took time to reproduce it with TDX. > >> > >> I will look what can be done. > > > > Could you check if the patch below helps? > > > > diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c > > index 853f7dc3c21d..591da3f368fa 100644 > > --- a/drivers/firmware/efi/unaccepted_memory.c > > +++ b/drivers/firmware/efi/unaccepted_memory.c > > @@ -8,6 +8,14 @@ > > /* Protects unaccepted memory bitmap */ > > static DEFINE_SPINLOCK(unaccepted_memory_lock); > > > > +struct accept_range { > > + struct list_head list; > > + unsigned long start; > > + unsigned long end; > > +}; > > + > > +static LIST_HEAD(accepting_list); > > + > > /* > > * accept_memory() -- Consult bitmap and accept the memory if needed. > > * > > @@ -24,6 +32,7 @@ void accept_memory(phys_addr_t start, phys_addr_t end) > > { > > struct efi_unaccepted_memory *unaccepted; > > unsigned long range_start, range_end; > > + struct accept_range range, *entry; > > unsigned long flags; > > u64 unit_size; > > > > @@ -80,7 +89,25 @@ void accept_memory(phys_addr_t start, phys_addr_t end) > > > > range_start = start / unit_size; > > > > + range.start = start; > > + range.end = end; > > +retry: > > spin_lock_irqsave(&unaccepted_memory_lock, flags); > > + > > + list_for_each_entry(entry, &accepting_list, list) { > > + if (entry->end < start) > > + continue; > > + if (entry->start > end) > > + continue; > > + spin_unlock_irqrestore(&unaccepted_memory_lock, flags); > > + > > + /* Somebody else accepting the range */ > > + cpu_relax(); > > Should this be rather cond_resched()? I think cpu_relax() isn't enough to > prevent soft lockups. Right. For some reason, I thought we cannot call cond_resched() from atomic context (we sometimes get there from atomic context), but we can. > Although IIUC hitting this should be rare, as the contending tasks will pick > different ranges via try_to_accept_memory_one(), right? Yes, it should be rare. Generally, with exception of memblock, we accept all memory with MAX_ORDER chunks. As long as unit_size <= MAX_ORDER page allocator should never trigger the conflict as the caller owns full range to accept. I will test the idea with larger unit_size to see how it behaves. -- Kiryl Shutsemau / Kirill A. Shutemov