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Date: Mon, 15 Jun 2020 10:28:58 +0200 From: Borislav Petkov <bp@...en8.de> To: Thadeu Lima de Souza Cascardo <cascardo@...onical.com> Cc: linux-kernel@...r.kernel.org, Mark Gross <mgross@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, John Johansen <john.johansen@...onical.com>, Steve Beattie <sbeattie@...ntu.com> Subject: Re: [PATCH] x86/speculation/srbds: do not try to turn mitigation off when not supported On Tue, Jun 09, 2020 at 02:43:13PM -0300, Thadeu Lima de Souza Cascardo wrote: > When SRBDS is mitigated by TSX OFF, update_srbds_msr will still read and Are you talking about this case in srbds_select_mitigation(): if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM)) srbds_mitigation = SRBDS_MITIGATION_TSX_OFF; ? and you have a system which: * Check to see if this is one of the MDS_NO systems supporting * TSX that are only exposed to SRBDS when TSX is enabled. i.e., no SRBDS microcode for it and the fix is to disable TSX? If so, I think the right fix should be to do: if (!boot_cpu_has(X86_FEATURE_SRBDS_CTRL)) return; in update_srbds_msr() with a comment above it explaining why that check is being done. Hmmm. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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