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

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Message-ID: <8e7f0a86-55e3-2974-75d6-50228ea179b3@amd.com>
Date:   Thu, 20 May 2021 12:44:50 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....com, 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 5/20/21 12:32 PM, Borislav Petkov wrote:
> 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.

Hmm, I use the SIZEMISMATCH later in the patches. Since I was
introducing the pvalidate in separate patch so decided to define all the
return code.


>> +#define PVALIDATE_FAIL_NOUPDATE		255 /* Software defined (when rFlags.CF = 1) */
> Put the comment above the define pls.

Noted.


>
>> +
>> +/* 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.

Noted.


>>  #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:

Noted.


> 	/* "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.
>