Re: [PATCH 2/2] x86/microcode: Rework early revisions reporting

Ashok Raj
2023-12-01T20:33:48Z

On Fri, Dec 01, 2023 at 05:39:28PM +0100, Borislav Petkov wrote:
> On Thu, Nov 30, 2023 at 10:34:31AM -0800, Ashok Raj wrote:
> > new_rev is always assigned even if there was no microcode to apply.
>
> That is wrong.
>
> In my defence, I don't have an Intel machine which has up-to-date
> microcode in the BIOS and the blob has the same microcode revision. All
> my Intel test boxes do update microcode.
>
> > - On AMD, the ucode is loaded even if the current revision matches what is
> > being loaded.
>
> From the commit message of the patch you're replying to:
>
> "What is also missing on the AMD side - something which people have
> requested before - is showing the microcode revision the CPU had
> *before* the early update."
>
> The logic is, we want to dump before-after everytime there was
> a successful early upload.
>
> > Currently, it's displayed as below:
> >
> > [ 113.395868] microcode: Current revision: 0x21000170
> > [ 113.404244] microcode: Updated early from: 0x21000170
>
> There's something else weird going on though. I would expect that that
> machine should not update microcode if it cannot find newer. Maybe the
> scan_microcode() logic is a bit weird still.
>
> Please run this debug + fix patch and send me full dmesg from that
> machine.
>

I'll get a dmesg shortly once i get my test system back.

What I meant was

void __init load_ucode_intel_bsp(struct early_load_data *ed)
{
struct ucode_cpu_info uci;

ed->old_rev = intel_get_microcode_revision();

uci.mc = get_microcode_blob(&uci, false);
if (uci.mc && apply_microcode_early(&uci) == UCODE_UPDATED)
ucode_patch_va = UCODE_BSP_LOADED;

ed->new_rev = uci.cpu_sig.rev;
}

ed->new_rev is always assigned, just not for the UCODE_UPDATED case. Hence
even if we had no microcode to update ed->new_rev ends up being non-zero.