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Date: Tue, 18 Feb 2025 13:39:02 +0100
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To: Proxmox VE development discussion <pve-devel@lists.proxmox.com>,
 Fiona Ebner <f.ebner@proxmox.com>
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From: Friedrich Weber <f.weber@proxmox.com>
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Subject: Re: [pve-devel] [PATCH qemu-server/manager/docs 0/3] close #5291:
 support disabling KSM for specific VMs
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On 17/02/2025 16:04, Fiona Ebner wrote:
> KSM exposes a guest's virtual memory to side-channel attacks. Add a VM
> configuration option to disable KSM for specific VMs that need to be
> protected against such attacks. This makes it possible to still
> benefit from KSM for other processes on the host rather than needing
> to turn of KSM completely.

As I had a KSM test setup available, I quickly tested this:

- created 4 VMs that, together, exceed 80% host RAM usage
- on one VM, set `allow-ksm=0` (tested via CLI and GUI)
- started VMs, monitored /proc/PID/ksm_stat
- only for the VM with `allow-ksm=0`, ksm_rmap_items/ksm_merging_pages
in ksm_stat stayed at 0. For all other VMs, both started to grow after a
couple of minutes.

So consider this:

Tested-by: Friedrich Weber <f.weber@proxmox.com>


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