linux-kernel - Re: [RFC v2-fix 1/1] x86/traps: Add #VE support for TDX guest

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Date:   Fri, 21 May 2021 11:45:35 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     Tony Luck <tony.luck@...el.com>, Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        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-fix 1/1] x86/traps: Add #VE support for TDX guest

Hi Dave,

On 5/17/21 5:09 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov"<kirill.shutemov@...ux.intel.com>
> 
> Virtualization Exceptions (#VE) are delivered to TDX guests due to
> specific guest actions which may happen in either user space or the kernel:
> 
>   * Specific instructions (WBINVD, for example)
>   * Specific MSR accesses
>   * Specific CPUID leaf accesses
>   * Access to TD-shared memory, which includes MMIO
> 
> In the settings that Linux will run in, virtual exceptions are never
> generated on accesses to normal, TD-private memory that has been
> accepted.
> 
> The entry paths do not access TD-shared memory, MMIO regions or use
> those specific MSRs, instructions, CPUID leaves that might generate #VE.
> 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.
> 
> After TDGETVEINFO #VE could happen in theory (e.g. through an NMI),
> although we don't expect it to happen because we don't expect NMIs to
> trigger #VEs. Another case where they could happen is if the #VE
> exception panics, but in this case there are no guarantees on anything
> anyways.
> 
> 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 which will result in an oops (and should eventually be a panic, as
> we would like to set panic_on_oops to 1 for TDX guests).
> 
> 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 ve_raise_fault() directly.
> ve_raise_fault() is similar to #GP handler and is responsible for
> sending SIGSEGV to userspace and cpu die and notifying debuggers and
> other die chain users.
> 
> Co-developed-by: Sean Christopherson<sean.j.christopherson@...el.com>
> Signed-off-by: Sean Christopherson<sean.j.christopherson@...el.com>
> Signed-off-by: Kirill A. Shutemov<kirill.shutemov@...ux.intel.com>
> Reviewed-by: Andi Kleen<ak@...ux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---

You have any other comments on this patch? If not, can you reply with your
Reviewed-by tag?

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer