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Message-ID: <facdf62c-d0b4-597d-a85d-5772ecaa2b86@redhat.com>
Date:   Wed, 20 Sep 2023 19:54:48 +0200
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Subject: Re: [PATCH v10 33/38] x86/entry: Add fred_entry_from_kvm() for VMX to
 handle IRQ/NMI
To:     Xin Li <xin3.li@intel.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org,
        linux-hyperv@vger.kernel.org, kvm@vger.kernel.org,
        xen-devel@lists.xenproject.org
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
        luto@kernel.org, seanjc@google.com, peterz@infradead.org,
        jgross@suse.com, ravi.v.shankar@intel.com, mhiramat@kernel.org,
        andrew.cooper3@citrix.com, jiangshanlai@gmail.com
References: <20230914044805.301390-1-xin3.li@intel.com>
 <20230914044805.301390-34-xin3.li@intel.com>
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From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <20230914044805.301390-34-xin3.li@intel.com>
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On 9/14/23 06:48, Xin Li wrote:
> +	/*
> +	 * Don't check the FRED stack level, the call stack leading to this
> +	 * helper is effectively constant and shallow (relatively speaking).

It's more that we don't need to protect from reentrancy.  The external 
interrupt uses stack level 0 so no adjustment would be needed anyway, 
and NMI does not use an IST even in the non-FRED case.

> +	 * Emulate the FRED-defined redzone and stack alignment.
> +	 */
> +	sub $(FRED_CONFIG_REDZONE_AMOUNT << 6), %rsp
> +	and $FRED_STACK_FRAME_RSP_MASK, %rsp