linux-kernel - Re: [RFC v2 08/32] x86/traps: Add #VE support for TDX guest

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Message-ID: <28e706d4-960e-a320-e8ea-84aff42ad6a4@intel.com>
Date:   Thu, 13 May 2021 13:14:11 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>
Cc:     Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC v2 08/32] x86/traps: Add #VE support for TDX guest

On 5/13/21 12:47 PM, Andi Kleen wrote:
> I don't see what could be added. If you have concrete suggestions please
> just propose something.

Oh, boy, I love writing changelogs!  I was hoping that the TDX folks
would chip in to write their own changelogs, but oh well.  You made my day!

--

Virtualization Exceptions (#VE) are delivered to TDX guests due to
specific guest actions which may happen in either userspace or the kernel:

 * Specific instructions (WBINVD, for example)
 * Specific MSR accesses
 * Specific CPUID leaf accesses
 * Access to TD-shared memory, which includes MMIO

#VE exceptions are never generated on accesses to normal, TD-private memory.

The entry paths do not access TD-shared memory or use those specific
MSRs, instructions, CPUID leaves.  In addition, all interrupts including
NMIs are blocked by the hardware starting with #VE delivery until
TDGETVEINFO is called.  This eliminates the chance of a #VE during the
syscall gap or paranoid entry paths and simplifies #VE handling.

If a guest kernel action which would normally cause a #VE occurs in the
interrupt-disabled region before TDGETVEINFO, a #DF is delivered to the
guest.

Add basic infrastructure to handle any #VE which occurs in the kernel or
userspace.  Later patches will add handling for specific #VE scenarios.

Convert unhandled #VE's (everything, until later in this series) so that
they appear just like a #GP by calling do_general_protection() directly.

--

Did I miss anything?