Re: [PATCH Part1 RFC v2 10/20] x86/sev: Add a helper for the PVALIDATE instruction

[Brijesh Singh]

On 4/30/21 7:16 AM, Brijesh Singh wrote:
> An SNP-active guest uses the PVALIDATE instruction to validate or
> rescind the validation of a guest page’s RMP entry. Upon completion,
> a return code is stored in EAX and rFLAGS bits are set based on the
> return code. If the instruction completed successfully, the CF
> indicates if the content of the RMP were changed or not.
>
> See AMD APM Volume 3 for additional details.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> ---
>  arch/x86/include/asm/sev.h | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 134a7c9d91b6..48f911a229ba 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -59,6 +59,16 @@ extern void vc_no_ghcb(void);
>  extern void vc_boot_ghcb(void);
>  extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
>  
> +/* Return code of pvalidate */
> +#define PVALIDATE_SUCCESS		0
> +#define PVALIDATE_FAIL_INPUT		1
> +#define PVALIDATE_FAIL_SIZEMISMATCH	6
> +#define PVALIDATE_FAIL_NOUPDATE		255 /* Software defined (when rFlags.CF = 1) */
> +
> +/* RMP page size */
> +#define RMP_PG_SIZE_2M			1
> +#define RMP_PG_SIZE_4K			0
> +
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  extern struct static_key_false sev_es_enable_key;
>  extern void __sev_es_ist_enter(struct pt_regs *regs);
> @@ -81,12 +91,29 @@ static __always_inline void sev_es_nmi_complete(void)
>  		__sev_es_nmi_complete();
>  }
>  extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
> +static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)
> +{
> +	unsigned long flags;
> +	int rc = 0;
> +
> +	asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFF\n\t"
> +		     CC_SET(c)
> +		     : CC_OUT(c) (flags), "=a"(rc)
> +		     : "a"(vaddr), "c"(rmp_psize), "d"(validate)
> +		     : "memory", "cc");
> +
> +	if (flags & X86_EFLAGS_CF)
> +		return PVALIDATE_FAIL_NOUPDATE;
> +
> +	return rc;
> +}


While generating the patches for part1, I accidentally picked the wrong
version of this patch.

The pvalidate() looks like this

static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool
validate)
{
    bool no_rmpupdate;
    int rc;

    asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFF\n\t"
             CC_SET(c)
             : CC_OUT(c) (no_rmpupdate), "=a"(rc)
             : "a"(vaddr), "c"(rmp_psize), "d"(validate)
             : "memory", "cc");

    if (no_rmpupdate)
        return PVALIDATE_FAIL_NOUPDATE;

    return rc;
}

https://github.com/AMDESE/linux/commit/581316923efb4e4833722962b02a0c892aed9505#diff-a9a713d4f58a64b6640506f689940cb077dcb0a3705da0c024145c0c857d6c38


>  #else
>  static inline void sev_es_ist_enter(struct pt_regs *regs) { }
>  static inline void sev_es_ist_exit(void) { }
>  static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { return 0; }
>  static inline void sev_es_nmi_complete(void) { }
>  static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
> +static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate) { return 0; }
>  #endif
>  
>  #endif