linux-kernel - Re: [RFC PATCH 14/32] x86/fred: header file with FRED definitions

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Date:   Tue, 20 Dec 2022 09:56:19 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Xin Li <xin3.li@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        andrew.cooper3@...rix.com, seanjc@...gle.com, pbonzini@...hat.com,
        ravi.v.shankar@...el.com
Subject: Re: [RFC PATCH 14/32] x86/fred: header file with FRED definitions


> +/*
> + * FRED return instructions
> + *
> + * Replace with "ERETS"/"ERETU" once binutils support FRED return instructions.

binutils version that supports these instructions goes here...

> + */
> +#define ERETS			_ASM_BYTES(0xf2,0x0f,0x01,0xca)
> +#define ERETU			_ASM_BYTES(0xf3,0x0f,0x01,0xca)
> +
> +/*
> + * Event stack level macro for the FRED_STKLVLS MSR.
> + * Usage example: FRED_STKLVL(X86_TRAP_DF, 3)
> + * Multiple values can be ORd together.
> + */
> +#define FRED_STKLVL(v,l)	(_AT(unsigned long, l) << (2*(v)))
> +
> +/* FRED_CONFIG MSR */
> +#define FRED_CONFIG_CSL_MASK		0x3
> +#define FRED_CONFIG_SHADOW_STACK_SPACE	_BITUL(3)
> +#define FRED_CONFIG_REDZONE(b)		__ALIGN_KERNEL_MASK((b), _UL(0x3f))
> +#define FRED_CONFIG_INT_STKLVL(l)	(_AT(unsigned long, l) << 9)
> +#define FRED_CONFIG_ENTRYPOINT(p)	_AT(unsigned long, (p))
> +
> +/* FRED event type and vector bit width and counts */
> +#define FRED_EVENT_TYPE_BITS		3 /* only 3 bits used in FRED 3.0 */
> +#define FRED_EVENT_TYPE_COUNT		_BITUL(FRED_EVENT_TYPE_BITS)
> +#define FRED_EVENT_VECTOR_BITS		8
> +#define FRED_EVENT_VECTOR_COUNT		_BITUL(FRED_EVENT_VECTOR_BITS)
> +
> +/* FRED EVENT_TYPE_OTHER vector numbers */
> +#define FRED_SYSCALL			1
> +#define FRED_SYSENTER			2
> +
> +/* Flags above the CS selector (regs->csl) */
> +#define FRED_CSL_ENABLE_NMI		_BITUL(28)
> +#define FRED_CSL_ALLOW_SINGLE_STEP	_BITUL(25)
> +#define FRED_CSL_INTERRUPT_SHADOW	_BITUL(24)

What's the state of IBT WAIT-FOR-ENDBR vs this? That really should also
get a high CS bit.