linux-kernel - Re: [PATCH v6 06/11] x86/traps: Add #VE support for TDX guest

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Message-ID: <00d97a18-0400-7785-5e62-92a968b52f75@intel.com>
Date:   Tue, 28 Sep 2021 08:25:27 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter H Anvin <hpa@...or.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 06/11] x86/traps: Add #VE support for TDX guest

On 9/28/21 8:22 AM, Joerg Roedel wrote:
> On Tue, Sep 28, 2021 at 07:05:40AM -0700, Dave Hansen wrote:
>> "Shared" pages can cause #VE's.  The guest must be careful not to touch
>> them in the syscall entry path, for example.  But, shared pages are
>> untrusted so they're not use for stacks.
>>
>> "Private" pages can cause #VE's.  But, only *some* of them.  Before a
>> page is accepted, it is in the SEPT_PENDING and a reference would cause
>> a #VE.  But, after acceptance, page references either succeed or a TD
>> Exit and the hypervisor gets to handle the situation.
> Okay, and there is no way for the VMM to replace an already accepted
> page with a page in SEPT_PENDING state?

I hope not.

There would be lots of other problems if that were permitted.