linux-kernel - Re: [PATCH v12 20/22] x86/virt/tdx: Allow SEAMCALL to handle #UD and #GP

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Message-ID: <20230628123229.byp3bl7husxt6eso@box.shutemov.name>
Date:   Wed, 28 Jun 2023 15:32:29 +0300
From:   kirill.shutemov@...ux.intel.com
To:     Kai Huang <kai.huang@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, dave.hansen@...el.com,
        tony.luck@...el.com, peterz@...radead.org, tglx@...utronix.de,
        bp@...en8.de, mingo@...hat.com, hpa@...or.com, seanjc@...gle.com,
        pbonzini@...hat.com, david@...hat.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, ashok.raj@...el.com,
        reinette.chatre@...el.com, len.brown@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, ying.huang@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, nik.borisov@...e.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v12 20/22] x86/virt/tdx: Allow SEAMCALL to handle #UD and
 #GP

On Tue, Jun 27, 2023 at 02:12:50AM +1200, Kai Huang wrote:
> On the platform with the "partial write machine check" erratum, a kernel
> partial write to TDX private memory may cause unexpected machine check.
> It would be nice if the #MC handler could print additional information
> to show the #MC was TDX private memory error due to possible kernel bug.
> 
> To do that, the machine check handler needs to use SEAMCALL to query
> page type of the error memory from the TDX module, because there's no
> existing infrastructure to track TDX private pages.
> 
> SEAMCALL instruction causes #UD if CPU isn't in VMX operation.  In #MC
> handler, it is legal that CPU isn't in VMX operation when making this
> SEAMCALL.  Extend the TDX_MODULE_CALL macro to handle #UD so the
> SEAMCALL can return error code instead of Oops in the #MC handler.
> Opportunistically handles #GP too since they share the same code.
> 
> A bonus is when kernel mistakenly calls SEAMCALL when CPU isn't in VMX
> operation, or when TDX isn't enabled by the BIOS, or when the BIOS is
> buggy, the kernel can get a nicer error message rather than a less
> understandable Oops.
> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov