Re: [PATCH v10 33/38] x86/entry: Add fred_entry_from_kvm() for VMX to handle IRQ/NMI

[Paolo Bonzini]

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