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

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Date:   Thu, 20 May 2021 19:32:42 +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 10/20] x86/sev: Add a helper for the
 PVALIDATE instruction

On Fri, Apr 30, 2021 at 08:05:36AM -0500, Brijesh Singh wrote:
> While generating the patches for part1, I accidentally picked the wrong
> version of this patch.

Adding the right one...

> Author: Brijesh Singh <brijesh.singh@....com>
> Date:   Thu Apr 29 16:45:36 2021 -0500
> 
>     x86/sev: Add a helper for the PVALIDATE instruction
>     
>     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@....com>
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 134a7c9d91b6..be67d9c70267 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

Those are unused. Remove them pls.

> +#define PVALIDATE_FAIL_NOUPDATE		255 /* Software defined (when rFlags.CF = 1) */

Put the comment above the define pls.

> +
> +/* RMP page size */
> +#define RMP_PG_SIZE_2M			1
> +#define RMP_PG_SIZE_4K			0

Add those when you need them - I see

[PATCH Part2 RFC v2 06/37] x86/sev: Add RMP entry lookup helpers

is moving them to some generic header. No need to add them to this patch
here.

>  #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)
> +{
> +	bool no_rmpupdate;
> +	int rc;

Adding this for the mail archives when we find this mail again in the
future so that I don't have to do binutils git archeology again:

Enablement for the "pvalidate" mnemonic is in binutils commit
646cc3e0109e ("Add AMD znver3 processor support"). :-)

Please put over the opcode bytes line:

	/* "pvalidate" mnemonic support in binutils 2.36 and newer */

> +
> +	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;
> +}

Thx.

-- 
Regards/Gruss,
    Boris.

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