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 15:04:42 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Mike Stunes <mstunes@...are.com>, 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>,
        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 4/14/20 2:03 PM, Mike Stunes wrote:
> 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.

At that point the guest won't be able to communicate with the hypervisor, 
too. Maybe we should BUG() here to terminate further processing?

Thanks,
Tom

>