linux-kernel - Re: [PATCH kernel 3/3] x86/sev: Do not handle #VC for DR7 read/write

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Message-ID: <Y4jmmfrUXAzydM0G@google.com>
Date:   Thu, 1 Dec 2022 17:38:33 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Alexey Kardashevskiy <aik@....com>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Venu Busireddy <venu.busireddy@...cle.com>,
        Tony Luck <tony.luck@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Michael Sterritt <sterritt@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH kernel 3/3] x86/sev: Do not handle #VC for DR7 read/write

On Thu, Dec 01, 2022, Alexey Kardashevskiy wrote:
> With SVM_SEV_FEAT_DEBUG_SWAP enabled, the VM should not get #VC events
> for DR7 read/write which it rather avoided.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@....com>
> ---
>  arch/x86/kernel/sev.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index a428c62330d3..4e91b9f8742c 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -1618,6 +1618,9 @@ static enum es_result vc_handle_dr7_write(struct ghcb *ghcb,
>  	long val, *reg = vc_insn_get_rm(ctxt);
>  	enum es_result ret;
>  
> +	if ((sev_status >> 2) & SVM_SEV_FEAT_DEBUG_SWAP)

Probably high time to add a helper/macro to convert the SEV_STATUS to the SEV_FEATURES
field.

> +		return ES_VMM_ERROR;
> +
>  	if (!reg)
>  		return ES_DECODE_FAILED;
>  
> @@ -1655,6 +1658,9 @@ static enum es_result vc_handle_dr7_read(struct ghcb *ghcb,
>  	struct sev_es_runtime_data *data = this_cpu_read(runtime_data);
>  	long *reg = vc_insn_get_rm(ctxt);
>  
> +	if ((sev_status >> 2) & SVM_SEV_FEAT_DEBUG_SWAP)
> +		return ES_VMM_ERROR;
> +
>  	if (!reg)
>  		return ES_DECODE_FAILED;
>  
> -- 
> 2.38.1
>