linux-kernel - Re: [PATCH v1 37/40] x86/cacheinfo: Extract out cache self-snoop checks

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Message-ID: <a2acde2d-d3bb-496d-bb65-e1ff322f13c4@citrix.com>
Date: Wed, 5 Mar 2025 19:01:46 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: "Ahmed S. Darwish" <darwi@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, John Ogness
 <john.ogness@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>,
 x86@...nel.org, x86-cpuid@...ts.linux.dev,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 37/40] x86/cacheinfo: Extract out cache self-snoop
 checks

On 05/03/2025 6:58 pm, Ahmed S. Darwish wrote:
> On Wed, 05 Mar 2025, Andrew Cooper wrote:
> ...
>> It turns out not to be safe in cases where the underlying physical
>> memory changes from cacheable to unchangeable.  By skipping the WBINVD
>> as part of changing the memory type, you end up with spurious writebacks
>> at a later point when the memory is expected to be UC.  Apparently this
>> is a problem for CLX devices, hence the change in the SDM.
> ...
>> CLX (Cascade Lake) != CXL (Compute eXpress Link).
>>
>> CXL is the new PCIe.  (So say the CXL consortium at least.)
>>
> Oh, sorry, you wrote "CLX devices" above, not CXL... Only thing my poor
> brain could come up with was CASCADELAKE_X :)

Oops, so I did.  Sorry.

~Andrew