linux-kernel - Re: [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime handler

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Date:   Tue, 14 Apr 2020 19:03:44 +0000
From:   Mike Stunes <mstunes@...are.com>
To:     Joerg Roedel <joro@...tes.org>
CC:     "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <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>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime
 handler

On Mar 19, 2020, at 2:13 AM, Joerg Roedel <joro@...tes.org> wrote:
> 
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> The runtime handler needs a GHCB per CPU. Set them up and map them
> unencrypted.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
> arch/x86/include/asm/mem_encrypt.h |  2 ++
> arch/x86/kernel/sev-es.c           | 28 +++++++++++++++++++++++++++-
> arch/x86/kernel/traps.c            |  3 +++
> 3 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index c17980e8db78..4bf5286310a0 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -197,6 +203,26 @@ static bool __init sev_es_setup_ghcb(void)
> 	return true;
> }
> 
> +void sev_es_init_ghcbs(void)
> +{
> +	int cpu;
> +
> +	if (!sev_es_active())
> +		return;
> +
> +	/* Allocate GHCB pages */
> +	ghcb_page = __alloc_percpu(sizeof(struct ghcb), PAGE_SIZE);
> +
> +	/* Initialize per-cpu GHCB pages */
> +	for_each_possible_cpu(cpu) {
> +		struct ghcb *ghcb = (struct ghcb *)per_cpu_ptr(ghcb_page, cpu);
> +
> +		set_memory_decrypted((unsigned long)ghcb,
> +				     sizeof(*ghcb) >> PAGE_SHIFT);
> +		memset(ghcb, 0, sizeof(*ghcb));
> +	}
> +}
> +

set_memory_decrypted needs to check the return value. I see it
consistently return ENOMEM. I've traced that back to split_large_page
in arch/x86/mm/pat/set_memory.c.