linux-kernel - Re: [PATCH v3] x86: Add a test for AMD SEV-ES guest #VC handling

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Message-ID: <77e09c12-0971-e5dc-7002-c88e30e9455e@suse.com>
Date:   Wed, 16 Jun 2021 11:16:59 +0200
From:   Varad Gautam <varad.gautam@...e.com>
To:     Joerg Roedel <jroedel@...e.de>
CC:     linux-kernel@...r.kernel.org, Varad Gautam <varad.gautam@...e.com>,
        kvm@...r.kernel.org, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v3] x86: Add a test for AMD SEV-ES guest #VC handling

On 6/9/21 4:50 PM, Joerg Roedel wrote:
> On Wed, Jun 02, 2021 at 04:14:47PM +0200, Varad Gautam wrote:
>> From: Varad Gautam <varad.gautam@...e.com>
>>
>> Some vmexits on a SEV-ES guest need special handling within the guest
>> before exiting to the hypervisor. This must happen within the guest's
>> \#VC exception handler, triggered on every non automatic exit.
>>
>> Add a KUnit based test to validate Linux's VC handling. The test:
>> 1. installs a kretprobe on the #VC handler (sev_es_ghcb_hv_call, to
>>    access GHCB before/after the resulting VMGEXIT).
>> 2. tiggers an NAE.
>> 3. checks that the kretprobe was hit with the right exit_code available
>>    in GHCB.
>>
>> Since relying on kprobes, the test does not cover NMI contexts.
>>
>> Signed-off-by: Varad Gautam <varad.gautam@...e.com>
>> ---
>>  arch/x86/Kconfig                 |   9 ++
>>  arch/x86/kernel/Makefile         |   8 ++
>>  arch/x86/kernel/sev-es-test-vc.c | 155 +++++++++++++++++++++++++++++++
> 
> This looks good to me except for the small comment below, thanks Varad.
> I ran it in an SEV-ES guest and I am seeing the test results in dmesg.
> Only thing I am missing is a 'rep movs' test for MMIO, but that can be
> added later, so
> 
> Tested-by: Joerg Roedel <jroedel@...e.de>
> 
> Btw, should we create a separate directory for such tests like
> /arch/x86/tests/ or something along those lines?
> 

Thanks, I've sent out a v4 with the test moved to arch/x86/tests. This is
now hidden behind a CONFIG_X86_TESTS, where more stuff can be plugged in.

>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 0045e1b441902..85b8ac450ba56 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1543,6 +1543,15 @@ config AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT
>>  	  If set to N, then the encryption of system memory can be
>>  	  activated with the mem_encrypt=on command line option.
>>  
>> +config AMD_SEV_ES_TEST_VC
>> +	bool "Test for AMD SEV-ES VC exception handling."
>> +	depends on AMD_MEM_ENCRYPT
>> +	select FUNCTION_TRACER
>> +	select KPROBES
>> +	select KUNIT
>> +	help
>> +	  Enable KUnit-based testing for AMD SEV-ES #VC exception handling.
>> +
> 
> I think this should be in arch/x86/Kconfig.debug.
> 
Ack, also moved in v4.

Varad

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