linux-kernel - Re: [RFC PATCH 3/7] x86/entry: Implement atomic-IST-entry

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Date:   Thu, 6 Apr 2023 23:58:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...nel.org>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Cfir Cohen <cfir@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        David Kaplan <David.Kaplan@....com>,
        David Rientjes <rientjes@...gle.com>,
        Dirk Hohndel <dirkhh@...are.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Jiri Slaby <jslaby@...e.cz>, Joerg Roedel <joro@...tes.org>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Stunes <mstunes@...are.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tony Luck <tony.luck@...el.com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH 3/7] x86/entry: Implement atomic-IST-entry

On Mon, Apr 03, 2023 at 10:06:01PM +0800, Lai Jiangshan wrote:
> +static __always_inline
> +void copy_regs_exception_head(struct pt_regs *target, const struct pt_regs *from)
> +{
> +	target->ss	= from->ss;
> +	target->sp	= from->sp;
> +	target->flags 	= from->flags;
> +	target->cs	= from->cs;
> +	target->ip	= from->ip;
> +	target->orig_ax	= from->orig_ax;
> +}
> +
> +static __always_inline
> +void copy_regs_general_registers(struct pt_regs *target, const struct pt_regs *from)
> +{
> +	target->di  = from->di;
> +	target->si  = from->si;
> +	target->dx  = from->dx;
> +	target->cx  = from->cx;
> +	target->ax  = from->ax;
> +	target->r8  = from->r8;
> +	target->r9  = from->r9;
> +	target->r10 = from->r10;
> +	target->r11 = from->r11;
> +	target->bx  = from->bx;
> +	target->bp  = from->bp;
> +	target->r12 = from->r12;
> +	target->r13 = from->r13;
> +	target->r14 = from->r14;
> +	target->r15 = from->r15;
> +}

> +/* Replicate the interrupted atomic-IST-entry's CLEAR_REGS macro. */
> +static __always_inline void replicate_clear_regs(struct pt_regs *target)
> +{
> +	target->di  = 0;
> +	target->si  = 0;
> +	target->dx  = 0;
> +	target->cx  = 0;
> +	target->ax  = 0;
> +	target->r8  = 0;
> +	target->r9  = 0;
> +	target->r10 = 0;
> +	target->r11 = 0;
> +	target->bx  = 0;
> +	target->bp  = 0;
> +	target->r12 = 0;
> +	target->r13 = 0;
> +	target->r14 = 0;
> +	target->r15 = 0;
> +}

I think there's compilers smart enough to see through your attempts at
avoiding mem{set,cpy}() there and I think we'll end up needing something
like __inline_memset() and __inline_memcpy() like here:

https://lore.kernel.org/lkml/Y759AJ%2F0N9fqwDED@hirez.programming.kicks-ass.net/