linux-kernel - Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section shared in RMP table

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Message-ID: <18eadf9d-8e31-0945-ccf4-2cb72b8e0dd4@amd.com>
Date:   Wed, 5 Jan 2022 13:52:14 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Venu Busireddy <venu.busireddy@...cle.com>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section
 shared in RMP table



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@....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
>