linux-kernel - Re: [PATCH v3 40/75] x86/sev-es: Compile early handler code into kernel image

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Message-ID: <20200520091415.GC1457@zn.tnic>
Date:   Wed, 20 May 2020 11:14:15 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 40/75] x86/sev-es: Compile early handler code into
 kernel image

On Tue, Apr 28, 2020 at 05:16:50PM +0200, Joerg Roedel wrote:
> +static inline u64 sev_es_rd_ghcb_msr(void)
> +{
> +	return native_read_msr(MSR_AMD64_SEV_ES_GHCB);
> +}
> +
> +static inline void sev_es_wr_ghcb_msr(u64 val)
> +{
> +	u32 low, high;
> +
> +	low  = (u32)(val);
> +	high = (u32)(val >> 32);
> +
> +	native_write_msr(MSR_AMD64_SEV_ES_GHCB, low, high);
> +}

Instead of duplicating those two, you can lift the ones in the
compressed image into sev-es.h and use them here. I don't care one bit
about the MSR tracepoints in native_*_msr().

> +static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
> +				   char *dst, char *buf, size_t size)
> +{
> +	unsigned long error_code = X86_PF_PROT | X86_PF_WRITE;
> +	char __user *target = (char __user *)dst;
> +	u64 d8;
> +	u32 d4;
> +	u16 d2;
> +	u8  d1;
> +
> +	switch (size) {
> +	case 1:
> +		memcpy(&d1, buf, 1);
> +		if (put_user(d1, target))
> +			goto fault;
> +		break;
> +	case 2:
> +		memcpy(&d2, buf, 2);
> +		if (put_user(d2, target))
> +			goto fault;
> +		break;
> +	case 4:
> +		memcpy(&d4, buf, 4);
> +		if (put_user(d4, target))
> +			goto fault;
> +		break;
> +	case 8:
> +		memcpy(&d8, buf, 8);
> +		if (put_user(d8, target))
> +			goto fault;

Ok, those (and below) memcpys get nicely optimized to MOVs by the
compiler here.

-- 
Regards/Gruss,
    Boris.

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