This is a note to let you know that I've just added the patch titled
x86/microcode: do not cache microcode if it will not be used
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-microcode-do-not-cache-microcode-if-it-will-not-be-used.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From pbonzini@xxxxxxxxxx Wed Jan 17 11:58:38 2024
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Mon, 15 Jan 2024 11:22:02 +0100
Subject: x86/microcode: do not cache microcode if it will not be used
To: linux-kernel@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, Borislav Petkov <bp@xxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Message-ID: <20240115102202.1321115-1-pbonzini@xxxxxxxxxx>
No relevant upstream kernel due to refactoring in 6.7
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().
Note that save_microcode_in_initrd() is not in the microcode application
path, which runs with paging disabled on 32-bit systems, so it can (and
has to) use dis_ucode_ldr instead of check_loader_disabled_ap().
Cc: stable@xxxxxxxxxxxxxxx # v6.6+
Cc: x86@xxxxxxxxxx # v6.6+
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Acked-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/microcode/core.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -208,6 +208,11 @@ static int __init save_microcode_in_init
struct cpuinfo_x86 *c = &boot_cpu_data;
int ret = -EINVAL;
+ if (dis_ucode_ldr) {
+ ret = 0;
+ goto out;
+ }
+
switch (c->x86_vendor) {
case X86_VENDOR_INTEL:
if (c->x86 >= 6)
@@ -221,6 +226,7 @@ static int __init save_microcode_in_init
break;
}
+out:
initrd_gone = true;
return ret;
Patches currently in stable-queue which might be from pbonzini@xxxxxxxxxx are
queue-6.6/x86-microcode-do-not-cache-microcode-if-it-will-not-be-used.patch
