linux-kernel - Re: [PATCH 07/11] treewide: Replace the use of mem_encrypt_active() with prot_guest

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Date:   Tue, 10 Aug 2021 14:48:54 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-graphics-maintainer@...are.com,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org
Cc:     Borislav Petkov <bp@...en8.de>,
        Brijesh Singh <brijesh.singh@....com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Will Deacon <will@...nel.org>, Dave Young <dyoung@...hat.com>,
        Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH 07/11] treewide: Replace the use of mem_encrypt_active()
 with prot_guest_has()

On 8/10/21 1:45 PM, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 7/27/21 3:26 PM, Tom Lendacky wrote:
>> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
>> index de01903c3735..cafed6456d45 100644
>> --- a/arch/x86/kernel/head64.c
>> +++ b/arch/x86/kernel/head64.c
>> @@ -19,7 +19,7 @@
>>   #include <linux/start_kernel.h>
>>   #include <linux/io.h>
>>   #include <linux/memblock.h>
>> -#include <linux/mem_encrypt.h>
>> +#include <linux/protected_guest.h>
>>   #include <linux/pgtable.h>
>>     #include <asm/processor.h>
>> @@ -285,7 +285,7 @@ unsigned long __head __startup_64(unsigned long
>> physaddr,
>>        * there is no need to zero it after changing the memory encryption
>>        * attribute.
>>        */
>> -    if (mem_encrypt_active()) {
>> +    if (prot_guest_has(PATTR_MEM_ENCRYPT)) {
>>           vaddr = (unsigned long)__start_bss_decrypted;
>>           vaddr_end = (unsigned long)__end_bss_decrypted;
> 
> 
> Since this change is specific to AMD, can you replace PATTR_MEM_ENCRYPT with
> prot_guest_has(PATTR_SME) || prot_guest_has(PATTR_SEV). It is not used in
> TDX.

This is a direct replacement for now. I think the change you're requesting
should be done as part of the TDX support patches so it's clear why it is
being changed.

But, wouldn't TDX still need to do something with this shared/unencrypted
area, though? Or since it is shared, there's actually nothing you need to
do (the bss decrpyted section exists even if CONFIG_AMD_MEM_ENCRYPT is not
configured)?

Thanks,
Tom

>