Re: [PATCH 11/12] x86/sev: Handle CLFLUSH MMIO events

[Sean Christopherson <seanjc@google.com>]

On Wed, Jul 21, 2021, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
> 
> Handle CLFLUSH instruction to MMIO memory in the #VC handler. The
                               ^
			       |- emulated

> instruction is ignored by the handler, as the Hypervisor is
> responsible for cache management of emulated MMIO memory.
> 
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>  arch/x86/kernel/sev-shared.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index a7a0793c4f98..682fa202444f 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -632,6 +632,15 @@ static enum es_result vc_handle_mmio_twobyte_ops(struct ghcb *ghcb,
>  	long *reg_data;
>  
>  	switch (insn->opcode.bytes[1]) {
> +		/* CLFLUSH */
> +	case 0xae:
> +		/*
> +		 * Ignore CLFLUSHes - those go to emulated MMIO anyway and the
> +		 * hypervisor is responsible for cache management.

This wording can be misread as "the hypervisor is responsible for _all_ cache
management".  Maybe just:

		/*
		 * Ignore CLFLUSHes - the hyperivsor is responsible for cache
		 * management of emulated MMIO.
		 */

Side topic, out of curisoity, what's mapping/accessing emulated MMIO as non-UC?

> +		 */
> +		ret = ES_OK;
> +		break;
> +
>  		/* MMIO Read w/ zero-extension */
>  	case 0xb6:
>  		bytes = 1;
> -- 
> 2.31.1
>