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Date:   Wed, 28 Jun 2023 15:32:29 +0300
From:   kirill.shutemov@linux.intel.com
To:     Kai Huang <kai.huang@intel.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
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Subject: Re: [PATCH v12 20/22] x86/virt/tdx: Allow SEAMCALL to handle #UD and
 #GP
Message-ID: <20230628123229.byp3bl7husxt6eso@box.shutemov.name>
References: <cover.1687784645.git.kai.huang@intel.com>
 <c124550719716f1f7759c2bdea70f4722d8e0167.1687784645.git.kai.huang@intel.com>
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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@intel.com>

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

-- 
  Kiryl Shutsemau / Kirill A. Shutemov