From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate001.proxmox.com (gate001.proxmox.com [45.144.208.40]) by lore.proxmox.com (Postfix) with ESMTPS id 780DD1FF0E5 for ; Wed, 15 Jul 2026 12:25:36 +0200 (CEST) Received: from gate001.proxmox.com (localhost.localdomain [127.0.0.1]) by gate001.proxmox.com (Proxmox) with ESMTP id 966662140A; Wed, 15 Jul 2026 12:25:35 +0200 (CEST) Message-ID: <1f8840f9-a651-41ff-b9f0-7c46fa26ed8b@proxmox.com> Date: Wed, 15 Jul 2026 12:25:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH] kernel config: don't automatically enable kexec handover (KHO) To: Dominik Csapak , pve-devel@lists.proxmox.com References: <20260714124456.347992-1-d.csapak@proxmox.com> Content-Language: en-US From: Thomas Lamprecht In-Reply-To: <20260714124456.347992-1-d.csapak@proxmox.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1784111111952 X-SPAM-LEVEL: Spam detection results: 0 AWL 0.322 Adjusted score from AWL reputation of From: address DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment (newer systems) KAM_SHORT 0.001 Use of a URL Shortener for very short URL RCVD_IN_DNSWL_LOW -0.7 Sender listed at https://www.dnswl.org/, low trust SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Message-ID-Hash: C75O6FL3AIOOBMS5RLXIXXS7KGREGCS3 X-Message-ID-Hash: C75O6FL3AIOOBMS5RLXIXXS7KGREGCS3 X-MailFrom: t.lamprecht@proxmox.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Am 14.07.26 um 14:44 schrieb Dominik Csapak: > CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT is enabled by default in the > upstream ubuntu kernel config, but has a (probably) unintended > side-effect: when KHO is automatically enabled, the kernel reserves > scratch memory for the kernel handoff and marks it with MIGRATE_CMA to > prevent non-movable allocations there. > > This causes unusual stats in /proc/meminfo, for example: > > CmaTotal: 0 kB > CmaFree: - > > which looks nonsensical on the surface. It also reduces the available > memory for e.g. guests with PCI passthrough, as pinner memory can't live > in these areas. > > Since we don't use kexec handover by default, and it can still be > enabled on the kernel commandline (kho=on), disable it by default to > increase the available pinnable memory for guests. We really should evaluate that though, IMO this [0] is the dream, and if it works, it might be used more compared to pcie passthrough. Also, is this actually reserved memory, or just mappings to have a linear address space available, when needed? [0]: https://lwn.net/Articles/1033364/ > > Signed-off-by: Dominik Csapak > --- > debian/rules.d/config-common.opts | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/debian/rules.d/config-common.opts b/debian/rules.d/config-common.opts > index 64505b4..204bab4 100644 > --- a/debian/rules.d/config-common.opts > +++ b/debian/rules.d/config-common.opts > @@ -68,3 +68,4 @@ > -d CONFIG_N_GSM > -d UBSAN_BOUNDS > -e CONFIG_RUST > +-d CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT