linux-kernel - Re: [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP

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Message-ID: <66db92101b565_22a229498@dwillia2-xfh.jf.intel.com.notmuch>
Date: Fri, 6 Sep 2024 16:36:48 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Kai Huang <kai.huang@...el.com>, <dave.hansen@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <tglx@...utronix.de>, <bp@...en8.de>,
	<peterz@...radead.org>, <mingo@...hat.com>, <hpa@...or.com>,
	<dan.j.williams@...el.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<rick.p.edgecombe@...el.com>, <isaku.yamahata@...el.com>,
	<chao.gao@...el.com>, <binbin.wu@...ux.intel.com>, <adrian.hunter@...el.com>,
	<kai.huang@...el.com>
Subject: Re: [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that
 doesn't support NO_RBP_MOD feature

How about:

    Subject: x86/virt/tdx: Require the module to assert it has the NO_RBP_MOD mitigation

...to avoid the double negative.

Kai Huang wrote:
> Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
> RBP is used as frame pointer in the x86_64 calling convention, and
> clobbering RBP could result in bad things like being unable to unwind
> the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
> gap.
> 
> A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
> not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
> metadata field via bit 18.
> 
> Don't initialize the TDX module if this feature is not supported [1].
> 
> Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]

Trim this to the direct message-id format, but otherwise:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>