Cc:     brijesh.singh@amd.com, x86@kernel.org,
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        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
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        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Borislav Petkov <bp@alien8.de>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
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        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section
 shared in RMP table
To:     Venu Busireddy <venu.busireddy@oracle.com>
References: <20211210154332.11526-1-brijesh.singh@amd.com>
 <20211210154332.11526-14-brijesh.singh@amd.com> <YdSKQKSTS83cRzGZ@dt>
From:   Brijesh Singh <brijesh.singh@amd.com>
Message-ID: <18eadf9d-8e31-0945-ccf4-2cb72b8e0dd4@amd.com>
Date:   Wed, 5 Jan 2022 13:52:14 -0600
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On 1/4/22 11:56 AM, Venu Busireddy wrote:
> On 2021-12-10 09:43:05 -0600, Brijesh Singh wrote:
>> The encryption attribute for the bss.decrypted region is cleared in the
>> initial page table build. This is because the section contains the data
>> that need to be shared between the guest and the hypervisor.
>>
>> When SEV-SNP is active, just clearing the encryption attribute in the
>> page table is not enough. The page state need to be updated in the RMP
>> table.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
>>   arch/x86/kernel/head64.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
>> index fa02402dcb9b..72c5082a3ba4 100644
>> --- a/arch/x86/kernel/head64.c
>> +++ b/arch/x86/kernel/head64.c
>> @@ -143,7 +143,14 @@ static unsigned long sme_postprocess_startup(struct boot_params *bp, pmdval_t *p
>>   	if (sme_get_me_mask()) {
>>   		vaddr = (unsigned long)__start_bss_decrypted;
>>   		vaddr_end = (unsigned long)__end_bss_decrypted;
>> +
>>   		for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
>> +			/*
>> +			 * When SEV-SNP is active then transition the page to shared in the RMP
>> +			 * table so that it is consistent with the page table attribute change.
>> +			 */
>> +			early_snp_set_memory_shared(__pa(vaddr), __pa(vaddr), PTRS_PER_PMD);
> 
> Shouldn't the first argument be vaddr as below?
> 

Nope, sme_postprocess_startup() is called while we are fixing the 
initial page table and running with identity mapping (so va == pa).

thanks

>     			early_snp_set_memory_shared(vaddr, __pa(vaddr), PTRS_PER_PMD);
> 
> Venu
>