linux-kernel - Re: [PATCH 2/2] x86/tdx: Do not allow #VE due to EPT violation on the private memory

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Message-ID: <4bfcd256-b926-9b1c-601c-efcff0d16605@intel.com>
Date:   Mon, 31 Oct 2022 07:22:36 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Guorui Yu <GuoRui.Yu@...ux.alibaba.com>,
        kirill.shutemov@...ux.intel.com
Cc:     ak@...ux.intel.com, bp@...en8.de, dan.j.williams@...el.com,
        david@...hat.com, elena.reshetova@...el.com, hpa@...or.com,
        linux-kernel@...r.kernel.org, luto@...nel.org, mingo@...hat.com,
        peterz@...radead.org, sathyanarayanan.kuppuswamy@...ux.intel.com,
        seanjc@...gle.com, tglx@...utronix.de, thomas.lendacky@....com,
        x86@...nel.org
Subject: Re: [PATCH 2/2] x86/tdx: Do not allow #VE due to EPT violation on the
 private memory

On 10/30/22 21:07, Guorui Yu wrote:
> We have encountered similar problems on SEV-ES, here are their fixes
> on Kernel [1] and OVMF[2].

SEV-ES and TDX are very different beasts in this area.

> Instead of enforcing the ATTR_SEPT_VE_DISABLE in TDX guest kernel, I
> think the fix should also include necessary check on the MMIO path of
> the #VE routine.

Instead?

Without ATTR_SEPT_VE_DISABLE, a #VE can occur on basically any
instruction.  We call those kinds of exceptions "paranoid entry" points.
 They need special handling like the NMI or #MC handlers.

I'd be happy to look at a patch that does the MMIO path check *and*
turns the #VE handler into a robust entry point.

Bonus points if you can do ~5 lines of C like the approach in this thread.