linux-kernel - Re: [PATCH v5 05/12] x86/tdx: Add __tdx_module_call() and __tdx

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Message-ID: <YR/HZuvry/xfDKDl@zn.tnic>
Date:   Fri, 20 Aug 2021 17:16:54 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 05/12] x86/tdx: Add __tdx_module_call() and
 __tdx_hypercall() helper functions

On Wed, Aug 04, 2021 at 11:13:22AM -0700, Kuppuswamy Sathyanarayanan wrote:
> +SYM_FUNC_START(__tdx_hypercall)
> +	FRAME_BEGIN
> +
> +	/* Move argument 7 from caller stack to RAX */
> +	movq ARG7_SP_OFFSET(%rsp), %rax
> +
> +	/* Check if caller provided an output struct */
> +	test %rax, %rax
> +	/* If out pointer is NULL, return -EINVAL */
> +	jz 1f
> +
> +	/* Save callee-s ved GPRs as mandated by the x86_64 ABI */

That should be "callee-saved" ofc. "s ved" is not a word. :-)

...

> +	/*
> +	 * Zero out registers exposed to the VMM to avoid
> +	 * speculative execution with VMM-controlled values.
> +	 * This needs to include all registers present in
> +	 * TDVMCALL_EXPOSE_REGS_MASK (except R12-R15).
> +	 * R12-R15 context will be restored.
> +	 */
> +	xor %r10d, %r10d
> +	xor %r11d, %r11d
> +
> +	/* Restore state of R9 register */
> +	pop %r9
> +
> +	/* Restore callee-s ved GPRs as mandated by the x86_64 ABI */

Here too.

Otherwise, LGTM. Thanks for documenting the ABI - looks good.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette