[pve-devel] [RFC kernel] revert problematic TSC multiplier commit

[Fiona Ebner]

Am 31.08.22 um 15:28 schrieb Fiona Ebner:
> which might be responsible for several issues reported in the
> community forum[0][1].
> 
> In my case, loading a VM snapshot that originally was taken on
> a CPU from a different vendor often caused problems in other VMs(!).
> In particular, it often led to RCU stalls (with similar messages as in
> [1]) or slowdowns, and sometimes clock jumps far into the future (like
> in [0]). With this revert applied, everything seems to run smoothly
> even after loading the "bad" snapshot 10 times.
> 
> [0] https://forum.proxmox.com/threads/112756/
> [1] https://forum.proxmox.com/threads/111494/
> 
> Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
> ---
> 
> Needed to build with an ABI bump, AFAICT because of the removed
> KVM_X86_OP(write_tsc_multiplier), but it's even an ABI break I guess?
> If this is not ok, we can either
> A) try to revert while keeping the ABI intact
> B) try to backport d1021a1bc47668aa715b7f2121086c9598bffcbf instead

Sorry, that's the hash in
git://git.launchpad.net/~ubuntu-kernel-test/ubuntu/+source/linux/+git/mainline-crack

Upstream it's 11d39e8cc43e1c6737af19ca9372e590061b5ad2

> 
> That's the one reason it's RFC. The other is that I haven't had much
> time to look at the actual code yet.
> 
>  ...dd-vendor-callbacks-for-writing-the-.patch | 247 ++++++++++++++++++
>  1 file changed, 247 insertions(+)
>  create mode 100644 patches/kernel/0032-Revert-KVM-X86-Add-vendor-callbacks-for-writing-the-.patch
> 
> diff --git a/patches/kernel/0032-Revert-KVM-X86-Add-vendor-callbacks-for-writing-the-.patch b/patches/kernel/0032-Revert-KVM-X86-Add-vendor-callbacks-for-writing-the-.patch
> new file mode 100644
> index 0000000..d2f7796
> --- /dev/null
> +++ b/patches/kernel/0032-Revert-KVM-X86-Add-vendor-callbacks-for-writing-the-.patch
> @@ -0,0 +1,247 @@
> +From 0747f18be1da2033a20c2a355678b9c278ce4603 Mon Sep 17 00:00:00 2001
> +From: Fiona Ebner <f.ebner at proxmox.com>
> +Date: Wed, 31 Aug 2022 13:49:55 +0200
> +Subject: [PATCH] Revert "KVM: X86: Add vendor callbacks for writing the TSC
> + multiplier"
> +
> +This reverts commit 1ab9287add5e265352d18517551abf6d01d004fd until commit
> +d1021a1bc47668aa715b7f2121086c9598bffcbf which fixes it can be cleanly

Same here

> +applied.
> +
> +Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>