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Message-ID: <c959d3ea-1187-3e88-287b-27e75f0225e8@amd.com>
Date: Wed, 27 Apr 2022 09:09:54 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Juergen Gross <jgross@...e.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 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.
TDX support also uses the arch_has_restricted_virtio_memory_access()
function and will need to be updated.
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?
Thanks,
Tom
>>>>
>>>> Huh, what does that have to do with SME?
>>>
>>> I picked the function where sev_status is being set, as this seemed to be
>>> the correct place to set the feature bit.
>>
>> What I don't understand is what does restricted memory access have to do
>> with AMD SEV and how does play together with what you guys are trying to
>> do?
>>
>> The big picture pls.
>
> Ah, okay.
>
> For support of virtio with Xen we want to not only support the virtio
> devices like KVM, but use grants for letting the guest decide which
> pages are allowed to be mapped by the backend (dom0).
>
> Instead of physical guest addresses the guest will use grant-ids (plus
> offset). In order to be able to handle this at the basic virtio level
> instead of the single virtio device drivers, we need to use dedicated
> dma-ops. And those will be used by virtio only, if the "restricted
> virtio memory request" flag is set, which is used by SEV, too. In order
> to let virtio set this flag, we need a way to communicate to virtio
> that the running system is either a SEV guest or a Xen guest.
>
> HTH,
>
>
> Juergen
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