Re: [PATCH Part1 RFC v3 12/22] x86/kernel: Make the bss.decrypted section shared in RMP table

From: Borislav Petkov <bp@alien8.de>
To: Brijesh Singh <brijesh.singh@amd.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-efi@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev,
	linux-mm@kvack.org, linux-crypto@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	tony.luck@intel.com, npmccallum@redhat.com
Subject: Re: [PATCH Part1 RFC v3 12/22] x86/kernel: Make the bss.decrypted section shared in RMP table
Date: Thu, 10 Jun 2021 18:06:15 +0200	[thread overview]
Message-ID: <YMI4dxkwes15c+lx@zn.tnic> (raw)
In-Reply-To: <20210602140416.23573-13-brijesh.singh@amd.com>

On Wed, Jun 02, 2021 at 09:04:06AM -0500, 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 de01903c3735..f4c3e632345a 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -288,7 +288,14 @@ unsigned long __head __startup_64(unsigned long physaddr,
>  	if (mem_encrypt_active()) {
>  		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);
> +
>  			i = pmd_index(vaddr);
>  			pmd[i] -= sme_get_me_mask();
>  		}
> -- 

It seems to me that all that code from the sme_encrypt_kernel(bp); call
to the end of the function should be in a separate function in sev.c
called sev_prepare_kernel(...args...) to be at least abstracted away
from the main boot path.

Thx.

-- 
Regards/Gruss,
    Boris.

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