linux-kernel - Re: [PATCH Part1 RFC v2 05/20] x86/sev: Define SNP Page State Change VMGEXIT structure

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Date:   Tue, 18 May 2021 12:41:08 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, jroedel@...e.de, thomas.lendacky@....com,
        pbonzini@...hat.com, mingo@...hat.com, dave.hansen@...el.com,
        rientjes@...gle.com, seanjc@...gle.com, peterz@...radead.org,
        hpa@...or.com, tony.luck@...el.com
Subject: Re: [PATCH Part1 RFC v2 05/20] x86/sev: Define SNP Page State Change
 VMGEXIT structure

On Fri, Apr 30, 2021 at 07:16:01AM -0500, Brijesh Singh wrote:
> An SNP-active guest will use the page state change NAE VMGEXIT defined in
> the GHCB specification to ask the hypervisor to make the guest page
> private or shared in the RMP table. In addition to the private/shared,
> the guest can also ask the hypervisor to split or combine multiple 4K
> validated pages as a single 2M page or vice versa.
> 
> See GHCB specification section Page State Change for additional
> information.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/asm/sev-common.h | 46 +++++++++++++++++++++++++++++++
>  arch/x86/include/uapi/asm/svm.h   |  2 ++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 8142e247d8da..07b8612bf182 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -67,6 +67,52 @@
>  #define GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION_TIMER		\
>  		(BIT_ULL(3) | GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION)
>  
> +/* SNP Page State Change */
> +#define GHCB_MSR_PSC_REQ		0x014
> +#define SNP_PAGE_STATE_PRIVATE		1
> +#define SNP_PAGE_STATE_SHARED		2
> +#define SNP_PAGE_STATE_PSMASH		3
> +#define SNP_PAGE_STATE_UNSMASH		4
> +#define GHCB_MSR_PSC_GFN_POS		12
> +#define GHCB_MSR_PSC_GFN_MASK		0xffffffffffULL

Why don't you use GENMASK_ULL() as I suggested? All those "f"s are
harder to count than seeing the start and end of a mask.

> +#define GHCB_MSR_PSC_OP_POS		52

Also, having defines for 12 and 52 doesn't make it more readable,
frankly.

When I see GENMASK_ULL(51, 12) it is kinda clear what it is. With the
defines, I have to go chase every define and replace it with the number
mentally.

> +#define GHCB_MSR_PSC_OP_MASK		0xf
> +#define GHCB_MSR_PSC_REQ_GFN(gfn, op) 	\
> +	(((unsigned long)((op) & GHCB_MSR_PSC_OP_MASK) << GHCB_MSR_PSC_OP_POS) | \
> +	(((gfn) << GHCB_MSR_PSC_GFN_POS) & GHCB_MSR_PSC_GFN_MASK) | GHCB_MSR_PSC_REQ)
> +
> +#define GHCB_MSR_PSC_RESP		0x015
> +#define GHCB_MSR_PSC_ERROR_POS		32
> +#define GHCB_MSR_PSC_ERROR_MASK		0xffffffffULL
> +#define GHCB_MSR_PSC_RSVD_POS		12
> +#define GHCB_MSR_PSC_RSVD_MASK		0xfffffULL
> +#define GHCB_MSR_PSC_RESP_VAL(val)	((val) >> GHCB_MSR_PSC_ERROR_POS)
> +
> +/* SNP Page State Change NAE event */
> +#define VMGEXIT_PSC_MAX_ENTRY		253
> +#define VMGEXIT_PSC_INVALID_HEADER	0x100000001
> +#define VMGEXIT_PSC_INVALID_ENTRY	0x100000002
> +#define VMGEXIT_PSC_FIRMWARE_ERROR(x)	((x & 0xffffffffULL) | 0x200000000)
> +
> +struct __packed snp_page_state_header {
> +	u16 cur_entry;
> +	u16 end_entry;
> +	u32 reserved;
> +};
> +
> +struct __packed snp_page_state_entry {
> +	u64 cur_page:12;
> +	u64 gfn:40;
> +	u64 operation:4;
> +	u64 pagesize:1;
> +	u64 reserved:7;

Please write it like this:

	u64 cur_page 	: 12,
	    gfn		: 40,
	    ...

to show that all those fields are part of the same u64.

struct perf_event_attr in include/uapi/linux/perf_event.h is a good
example.

> +};
> +
> +struct __packed snp_page_state_change {
> +	struct snp_page_state_header header;
> +	struct snp_page_state_entry entry[VMGEXIT_PSC_MAX_ENTRY];
> +};
> +
>  #define GHCB_MSR_TERM_REQ		0x100
>  #define GHCB_MSR_TERM_REASON_SET_POS	12
>  #define GHCB_MSR_TERM_REASON_SET_MASK	0xf
> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
> index 7fbc311e2de1..f7bf12cad58c 100644
> --- a/arch/x86/include/uapi/asm/svm.h
> +++ b/arch/x86/include/uapi/asm/svm.h
> @@ -108,6 +108,7 @@
>  #define SVM_VMGEXIT_AP_JUMP_TABLE		0x80000005
>  #define SVM_VMGEXIT_SET_AP_JUMP_TABLE		0
>  #define SVM_VMGEXIT_GET_AP_JUMP_TABLE		1
> +#define SVM_VMGEXIT_SNP_PAGE_STATE_CHANGE	0x80000010

SVM_VMGEXIT_SNP_PSC

>  #define SVM_VMGEXIT_HYPERVISOR_FEATURES		0x8000fffd
>  #define SVM_VMGEXIT_UNSUPPORTED_EVENT		0x8000ffff
>  
> @@ -216,6 +217,7 @@
>  	{ SVM_VMGEXIT_NMI_COMPLETE,	"vmgexit_nmi_complete" }, \
>  	{ SVM_VMGEXIT_AP_HLT_LOOP,	"vmgexit_ap_hlt_loop" }, \
>  	{ SVM_VMGEXIT_AP_JUMP_TABLE,	"vmgexit_ap_jump_table" }, \
> +	{ SVM_VMGEXIT_SNP_PAGE_STATE_CHANGE,	"vmgexit_page_state_change" }, \

Ditto.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette