linux-kernel - Re: [PATCH v10 33/38] x86/entry: Add fred_entry_from

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Date:   Wed, 20 Sep 2023 19:54:48 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Xin Li <xin3.li@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
        linux-hyperv@...r.kernel.org, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        luto@...nel.org, seanjc@...gle.com, peterz@...radead.org,
        jgross@...e.com, ravi.v.shankar@...el.com, mhiramat@...nel.org,
        andrew.cooper3@...rix.com, jiangshanlai@...il.com
Subject: Re: [PATCH v10 33/38] x86/entry: Add fred_entry_from_kvm() for VMX to
 handle IRQ/NMI

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