linux-kernel - Re: [PATCH Part2 v6 06/49] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction

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Date:   Tue, 21 Jun 2022 17:40:17 +0100
From:   "Dr. David Alan Gilbert" <dgilbert@...hat.com>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
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        alpergun@...gle.com, jarkko@...nel.org
Subject: Re: [PATCH Part2 v6 06/49] x86/sev: Add helper functions for
 RMPUPDATE and PSMASH instruction

* Ashish Kalra (Ashish.Kalra@....com) wrote:
> From: Brijesh Singh <brijesh.singh@....com>
> 
> The RMPUPDATE instruction writes a new RMP entry in the RMP Table. The
> hypervisor will use the instruction to add pages to the RMP table. See
> APM3 for details on the instruction operations.
> 
> The PSMASH instruction expands a 2MB RMP entry into a corresponding set of
> contiguous 4KB-Page RMP entries. The hypervisor will use this instruction
> to adjust the RMP entry without invalidating the previous RMP entry.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/asm/sev.h | 11 ++++++
>  arch/x86/kernel/sev.c      | 72 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 83 insertions(+)
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index cb16f0e5b585..6ab872311544 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -85,7 +85,9 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
>  
>  /* RMP page size */
>  #define RMP_PG_SIZE_4K			0
> +#define RMP_PG_SIZE_2M			1
>  #define RMP_TO_X86_PG_LEVEL(level)	(((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)
> +#define X86_TO_RMP_PG_LEVEL(level)	(((level) == PG_LEVEL_4K) ? RMP_PG_SIZE_4K : RMP_PG_SIZE_2M)
>  
>  /*
>   * The RMP entry format is not architectural. The format is defined in PPR
> @@ -126,6 +128,15 @@ struct snp_guest_platform_data {
>  	u64 secrets_gpa;
>  };
>  
> +struct rmpupdate {
> +	u64 gpa;
> +	u8 assigned;
> +	u8 pagesize;
> +	u8 immutable;
> +	u8 rsvd;
> +	u32 asid;
> +} __packed;

I see above it says the RMP entry format isn't architectural; is this
'rmpupdate' structure? If not how is this going to get handled when we
have a couple of SNP capable CPUs with different layouts?

Dave

>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  extern struct static_key_false sev_es_enable_key;
>  extern void __sev_es_ist_enter(struct pt_regs *regs);
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 59e7ec6b0326..f6c64a722e94 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -2429,3 +2429,75 @@ int snp_lookup_rmpentry(u64 pfn, int *level)
>  	return !!rmpentry_assigned(e);
>  }
>  EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);
> +
> +int psmash(u64 pfn)
> +{
> +	unsigned long paddr = pfn << PAGE_SHIFT;
> +	int ret;
> +
> +	if (!pfn_valid(pfn))
> +		return -EINVAL;
> +
> +	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> +		return -ENXIO;
> +
> +	/* Binutils version 2.36 supports the PSMASH mnemonic. */
> +	asm volatile(".byte 0xF3, 0x0F, 0x01, 0xFF"
> +		      : "=a"(ret)
> +		      : "a"(paddr)
> +		      : "memory", "cc");
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(psmash);
> +
> +static int rmpupdate(u64 pfn, struct rmpupdate *val)
> +{
> +	unsigned long paddr = pfn << PAGE_SHIFT;
> +	int ret;
> +
> +	if (!pfn_valid(pfn))
> +		return -EINVAL;
> +
> +	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> +		return -ENXIO;
> +
> +	/* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
> +	asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
> +		     : "=a"(ret)
> +		     : "a"(paddr), "c"((unsigned long)val)
> +		     : "memory", "cc");
> +	return ret;
> +}
> +
> +int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid, bool immutable)
> +{
> +	struct rmpupdate val;
> +
> +	if (!pfn_valid(pfn))
> +		return -EINVAL;
> +
> +	memset(&val, 0, sizeof(val));
> +	val.assigned = 1;
> +	val.asid = asid;
> +	val.immutable = immutable;
> +	val.gpa = gpa;
> +	val.pagesize = X86_TO_RMP_PG_LEVEL(level);
> +
> +	return rmpupdate(pfn, &val);
> +}
> +EXPORT_SYMBOL_GPL(rmp_make_private);
> +
> +int rmp_make_shared(u64 pfn, enum pg_level level)
> +{
> +	struct rmpupdate val;
> +
> +	if (!pfn_valid(pfn))
> +		return -EINVAL;
> +
> +	memset(&val, 0, sizeof(val));
> +	val.pagesize = X86_TO_RMP_PG_LEVEL(level);
> +
> +	return rmpupdate(pfn, &val);
> +}
> +EXPORT_SYMBOL_GPL(rmp_make_shared);
> -- 
> 2.25.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@...hat.com / Manchester, UK