linux-kernel - Re: [PATCH 2/2] virtio: replace arch_has_restricted_virtio_memory

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Date:   Wed, 27 Apr 2022 16:14:14 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-arch@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Oleksandr Tyshchenko <olekstysh@...il.com>
Subject: Re: [PATCH 2/2] virtio: replace
 arch_has_restricted_virtio_memory_access()

On 27.04.22 16:09, Tom Lendacky wrote:
> On 4/27/22 07:37, Juergen Gross wrote:
>> On 27.04.22 14:28, Borislav Petkov wrote:
>>> On Wed, Apr 27, 2022 at 08:37:31AM +0200, Juergen Gross wrote:
>>>> On 26.04.22 19:35, Borislav Petkov wrote:
>>>>> On Tue, Apr 26, 2022 at 03:40:21PM +0200, Juergen Gross wrote:
>>>>>>    /* protected virtualization */
>>>>>>    static void pv_init(void)
>>>>>>    {
>>>>>>        if (!is_prot_virt_guest())
>>>>>>            return;
>>>>>> +    platform_set_feature(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
>>>>>
>>>>> Kinda long-ish for my taste. I'll probably call it:
>>>>>
>>>>>     platform_set()
>>>>>
>>>>> as it is implicit that it sets a feature bit.
>>>>
>>>> Okay, fine with me.
>>>>
>>>>>
>>>>>> diff --git a/arch/x86/mm/mem_encrypt_identity.c 
>>>>>> b/arch/x86/mm/mem_encrypt_identity.c
>>>>>> index b43bc24d2bb6..6043ba6cd17d 100644
>>>>>> --- a/arch/x86/mm/mem_encrypt_identity.c
>>>>>> +++ b/arch/x86/mm/mem_encrypt_identity.c
>>>>>> @@ -40,6 +40,7 @@
>>>>>>    #include <linux/mm.h>
>>>>>>    #include <linux/mem_encrypt.h>
>>>>>>    #include <linux/cc_platform.h>
>>>>>> +#include <linux/platform-feature.h>
>>>>>>    #include <asm/setup.h>
>>>>>>    #include <asm/sections.h>
>>>>>> @@ -566,6 +567,10 @@ void __init sme_enable(struct boot_params *bp)
>>>>>>        } else {
>>>>>>            /* SEV state cannot be controlled by a command line option */
>>>>>>            sme_me_mask = me_mask;
>>>>>> +
>>>>>> +        /* Set restricted memory access for virtio. */
>>>>>> +        platform_set_feature(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
> 
> This is way early in the boot, but it appears that marking the platform feature 
> bitmap as __read_mostly puts this in the .data section, so avoids the issue of 
> bss being cleared.

In V2 (not yet posted) I have moved the call to sev_setup_arch().

> 
> TDX support also uses the arch_has_restricted_virtio_memory_access() function 
> and will need to be updated.

Yes.

> Seems like a lot of changes, I just wonder if the the arch_has...() function 
> couldn't be updated to also include a Xen check?

This was not seen to be a nice solution.

And TBH, I think this series is making the code much cleaner. Look at the
diffstat of this patch.


Juergen

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