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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Xin Li <xin3.li@intel.com>, linux-kernel@vger.kernel.org,
        x86@kernel.org, kvm@vger.kernel.org
Cc:     mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, peterz@infradead.org, andrew.cooper3@citrix.com,
        seanjc@google.com, pbonzini@redhat.com, ravi.v.shankar@intel.com,
        jiangshanlai@gmail.com, shan.kang@intel.com
Subject: Re: [PATCH v8 31/33] x86/fred: BUG() when ERETU with %rsp not equal
 to that when the ring 3 event was just delivered
In-Reply-To: <20230410081438.1750-32-xin3.li@intel.com>
References: <20230410081438.1750-1-xin3.li@intel.com>
 <20230410081438.1750-32-xin3.li@intel.com>
Date:   Mon, 05 Jun 2023 16:15:18 +0200
Message-ID: <87ttvm572h.ffs@tglx>
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On Mon, Apr 10 2023 at 01:14, Xin Li wrote:
> A FRED stack frame generated by a ring 3 event should never be messed up, and
> the first thing we must make sure is that at the time an ERETU instruction is
> executed, %rsp must have the same address as that when the user level event
> was just delivered.
>
> However we don't want to bother the normal code path of ERETU because it's on
> the hotest code path, a good choice is to do this check when ERETU
> faults.

Which might be not catching bugs where the wrong frame makes ERETU not
fault.

We have CONFIG_DEBUG_ENTRY for catching this at the proper place.

Thanks,

        tglx