From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate001.proxmox.com (gate001.proxmox.com [IPv6:2a0f:8001:1:32::40]) by lore.proxmox.com (Postfix) with ESMTPS id C6D8C1FF12F for ; Wed, 15 Jul 2026 10:13:12 +0200 (CEST) Received: from gate001.proxmox.com (localhost.localdomain [127.0.0.1]) by gate001.proxmox.com (Proxmox) with ESMTP id 8F36121419; Wed, 15 Jul 2026 10:13:10 +0200 (CEST) Message-ID: <72daae70-d63c-44b6-a461-d39481ee351b@proxmox.com> Date: Wed, 15 Jul 2026 10:12:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH] kernel config: don't automatically enable kexec handover (KHO) From: Dominik Csapak To: pve-devel@lists.proxmox.com References: <20260714124456.347992-1-d.csapak@proxmox.com> Content-Language: en-US In-Reply-To: <20260714124456.347992-1-d.csapak@proxmox.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1784103136843 X-SPAM-LEVEL: Spam detection results: 0 AWL 0.336 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) 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: 3LO2IFMQGYFE54A4MAOIG4YJSNA527JF X-Message-ID-Hash: 3LO2IFMQGYFE54A4MAOIG4YJSNA527JF X-MailFrom: d.csapak@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: just a note for this (maybe can be squashed into the commit message on applying): this does not disable the kexec handoff completely, it just does not enable it by default, so users that would need it can still enable it via 'kho=on' on the commandline. conversely, users running into problem with the current configuration can mitigate the issue by adding 'kho=off' to their commandline to disable it. On 7/14/26 2:44 PM, Dominik Csapak wrote: > 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: 4894720 kB > > 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. > > 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