linux-kernel - Re: [PATCH stable] x86/microcode: do not cache microcode if it will not be used

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Date: Mon, 15 Jan 2024 19:35:48 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org, x86@...nel.org,
	Borislav Petkov <bp@...e.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH stable] x86/microcode: do not cache microcode if it will
 not be used

On Mon, Jan 15, 2024 at 11:22:02AM +0100, Paolo Bonzini wrote:
> [ Upstream commit a7939f01672034a58ad3fdbce69bb6c665ce0024 ]

This really isn't this commit id, sorry.

> Builtin/initrd microcode will not be used the ucode loader is disabled.
> But currently, save_microcode_in_initrd is always performed and it
> accesses MSR_IA32_UCODE_REV even if dis_ucode_ldr is true, and in
> particular even if X86_FEATURE_HYPERVISOR is set; the TDX module does not
> implement the MSR and the result is a call trace at boot for TDX guests.
> 
> Mainline Linux fixed this as part of a more complex rework of microcode
> caching that went into 6.7 (see in particular commits dd5e3e3ca6,
> "x86/microcode/intel: Simplify early loading"; and a7939f0167203,
> "x86/microcode/amd: Cache builtin/initrd microcode early").  Do the bare
> minimum in stable kernels, setting initrd_gone just like mainline Linux
> does in mark_initrd_gone().

Why can't we take the changes in 6.7?  Doing a one-off almost always
causes problems :(

What exact commits are needed?

thanks,

greg