Re: [PATCH v4 5/8] x86/sev: Map only the RMP table entries instead of the full RMP range

["Kalra, Ashish" <ashish.kalra@amd.com>]

On 10/23/2024 1:41 PM, Tom Lendacky wrote:
> In preparation for support of a segmented RMP table, map only the RMP
> table entries. The RMP bookkeeping area is only ever accessed when
> first enabling SNP and does not need to remain mapped. To accomplish
> this, split the initialization of the RMP bookkeeping area and the
> initialization of the RMP entry area. The RMP bookkeeping area will be
> mapped only while it is being initialized.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  arch/x86/virt/svm/sev.c | 36 +++++++++++++++++++++++++++++++-----
>  1 file changed, 31 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> index d0fca9bb2e12..dd256e76e443 100644
> --- a/arch/x86/virt/svm/sev.c
> +++ b/arch/x86/virt/svm/sev.c
> @@ -168,6 +168,23 @@ void __init snp_fixup_e820_tables(void)
>  	__snp_fixup_e820_tables(probed_rmp_base + probed_rmp_size);
>  }
>  
> +static bool __init init_rmptable_bookkeeping(void)
> +{
> +	void *bk;
> +
> +	bk = memremap(probed_rmp_base, RMPTABLE_CPU_BOOKKEEPING_SZ, MEMREMAP_WB);
> +	if (!bk) {
> +		pr_err("Failed to map RMP bookkeeping area\n");
> +		return false;
> +	}
> +
> +	memset(bk, 0, RMPTABLE_CPU_BOOKKEEPING_SZ);
> +
> +	memunmap(bk);
> +
> +	return true;
> +}
> +
>  /*
>   * Do the necessary preparations which are verified by the firmware as
>   * described in the SNP_INIT_EX firmware command description in the SNP
> @@ -205,12 +222,17 @@ static int __init snp_rmptable_init(void)
>  		goto nosnp;
>  	}
>  
> -	rmptable_start = memremap(probed_rmp_base, probed_rmp_size, MEMREMAP_WB);
> +	/* Map only the RMP entries */
> +	rmptable_start = memremap(probed_rmp_base + RMPTABLE_CPU_BOOKKEEPING_SZ,
> +				  probed_rmp_size - RMPTABLE_CPU_BOOKKEEPING_SZ,
> +				  MEMREMAP_WB);
>  	if (!rmptable_start) {
>  		pr_err("Failed to map RMP table\n");
>  		goto nosnp;
>  	}
>  
> +	rmptable_size = probed_rmp_size - RMPTABLE_CPU_BOOKKEEPING_SZ;
> +
>  	/*
>  	 * Check if SEV-SNP is already enabled, this can happen in case of
>  	 * kexec boot.
> @@ -219,7 +241,14 @@ static int __init snp_rmptable_init(void)
>  	if (val & MSR_AMD64_SYSCFG_SNP_EN)
>  		goto skip_enable;
>  
> -	memset(rmptable_start, 0, probed_rmp_size);
> +	/* Zero out the RMP bookkeeping area */
> +	if (!init_rmptable_bookkeeping()) {
> +		memunmap(rmptable_start);
> +		goto nosnp;
> +	}
> +
> +	/* Zero out the RMP entries */
> +	memset(rmptable_start, 0, rmptable_size);
>  
>  	/* Flush the caches to ensure that data is written before SNP is enabled. */
>  	wbinvd_on_all_cpus();
> @@ -230,9 +259,6 @@ static int __init snp_rmptable_init(void)
>  	on_each_cpu(snp_enable, NULL, 1);
>  
>  skip_enable:
> -	rmptable_start += RMPTABLE_CPU_BOOKKEEPING_SZ;
> -	rmptable_size = probed_rmp_size - RMPTABLE_CPU_BOOKKEEPING_SZ;
> -
>  	rmptable = (struct rmpentry *)rmptable_start;
>  	rmptable_max_pfn = rmptable_size / sizeof(struct rmpentry) - 1;
>  

Reviewed-by: Ashish Kalra <ashish.kalra@amd.com>

Thanks,
Ashish