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

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Date:   Wed, 9 Jun 2021 16:50:28 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Varad Gautam <varadgautam@...il.com>
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 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?

> 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.