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 13:09:02 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....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>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 07/11] treewide: Replace the use of mem_encrypt_active()
 with prot_guest_has()



On 8/10/21 12:48 PM, Tom Lendacky wrote:
> 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.

Ok. I will include it part of TDX changes.

> 
> 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)?

Kirill had a requirement to turn on CONFIG_AMD_MEM_ENCRYPT for adding lazy
accept support in TDX guest kernel. Kirill, can you add details here?

> 
> Thanks,
> Tom
> 
>>

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer