From: Brijesh Singh <brijesh.singh@amd.com>
To: Tom Lendacky <thomas.lendacky@amd.com>, Borislav Petkov <bp@alien8.de>
Cc: brijesh.singh@amd.com, linux-kernel@vger.kernel.org,
x86@kernel.org, kvm@vger.kernel.org, ak@linux.intel.com,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
"H. Peter Anvin" <hpa@zytor.com>, Tony Luck <tony.luck@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Paolo Bonzini <pbonzini@redhat.com>,
David Rientjes <rientjes@google.com>,
Sean Christopherson <seanjc@google.com>
Subject: Re: [RFC Part1 PATCH 06/13] x86/compressed: rescinds and validate the memory used for the GHCB
Date: Wed, 7 Apr 2021 12:15:42 -0500 [thread overview]
Message-ID: <cda55ba3-cb74-60d2-8591-0592093c5223@amd.com> (raw)
In-Reply-To: <205cb304-8066-5049-9952-aac930cceb24@amd.com>
On 4/7/21 9:21 AM, Tom Lendacky wrote:
> On 4/7/21 8:35 AM, Brijesh Singh wrote:
>> On 4/7/21 6:16 AM, Borislav Petkov wrote:
>>> On Tue, Apr 06, 2021 at 10:47:18AM -0500, Brijesh Singh wrote:
>>>> Before the GHCB is established the caller does not need to save and
>>>> restore MSRs. The page_state_change() uses the GHCB MSR protocol and it
>>>> can be called before and after the GHCB is established hence I am saving
>>>> and restoring GHCB MSRs.
>>> I think you need to elaborate on that, maybe with an example. What the
>>> other sites using the GHCB MSR currently do is:
>>>
>>> 1. request by writing it
>>> 2. read the response
>>>
>>> None of them save and restore it.
>>>
>>> So why here?
>> GHCB provides two ways to exit from the guest to the hypervisor. The MSR
>> protocol and NAEs. The MSR protocol is generally used before the GHCB is
>> established. After the GHCB is established the guests typically uses the
>> NAEs. All of the current call sites uses the MSR protocol before the
>> GHCB is established so they do not need to save and restore the GHCB.
>> The GHCB is established on the first #VC -
>> arch/x86/boot/compressed/sev-es.c early_setup_sev_es(). The GHCB page
>> must a shared page:
>>
>> early_setup_sev_es()
>>
>> set_page_decrypted()
>>
>> sev_snp_set_page_shared()
>>
>> The sev_snp_set_page_shared() called before the GHCB is established.
>> While exiting from the decompression the sev_es_shutdown_ghcb() is
>> called to deinit the GHCB.
>>
>> sev_es_shutdown_ghcb()
>>
>> set_page_encrypted()
>>
>> sev_snp_set_page_private()
>>
>> Now that sev_snp_set_private() is called after the GHCB is established.
> I believe the current SEV-ES code always sets the GHCB address in the GHCB
> MSR before invoking VMGEXIT, so I think you're safe either way. Worth
> testing at least.
Ah, I didn;t realize that the sev_es_ghcb_hv_call() helper sets the GHCB
MSR before invoking VMGEXIT. I should be able to drop the save and
restore during the page state change. Thanks Tom.
next prev parent reply other threads:[~2021-04-07 17:15 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-24 16:44 [RFC Part1 PATCH 00/13] Add AMD Secure Nested Paging (SEV-SNP) Guest Support Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 01/13] x86/cpufeatures: Add SEV-SNP CPU feature Brijesh Singh
2021-03-25 10:54 ` Borislav Petkov
2021-03-25 14:50 ` Brijesh Singh
2021-03-25 16:29 ` Borislav Petkov
2021-03-24 16:44 ` [RFC Part1 PATCH 02/13] x86/mm: add sev_snp_active() helper Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 03/13] x86: add a helper routine for the PVALIDATE instruction Brijesh Singh
2021-03-26 14:30 ` Borislav Petkov
2021-03-26 15:42 ` Brijesh Singh
2021-03-26 18:22 ` Brijesh Singh
2021-03-26 19:12 ` Borislav Petkov
2021-03-26 20:04 ` Brijesh Singh
2021-03-26 19:22 ` Borislav Petkov
2021-03-26 20:01 ` Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 04/13] x86/sev-snp: define page state change VMGEXIT structure Brijesh Singh
2021-04-01 10:32 ` Borislav Petkov
2021-04-01 14:11 ` Brijesh Singh
2021-04-02 15:44 ` Borislav Petkov
2021-03-24 16:44 ` [RFC Part1 PATCH 05/13] X86/sev-es: move few helper functions in common file Brijesh Singh
2021-04-02 19:27 ` Borislav Petkov
2021-04-02 21:33 ` Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 06/13] x86/compressed: rescinds and validate the memory used for the GHCB Brijesh Singh
2021-04-06 10:33 ` Borislav Petkov
2021-04-06 15:47 ` Brijesh Singh
2021-04-06 19:42 ` Tom Lendacky
2021-04-07 11:25 ` Borislav Petkov
2021-04-07 19:45 ` Borislav Petkov
2021-04-08 13:57 ` Tom Lendacky
2021-04-07 11:16 ` Borislav Petkov
2021-04-07 13:35 ` Brijesh Singh
2021-04-07 14:21 ` Tom Lendacky
2021-04-07 17:15 ` Brijesh Singh [this message]
2021-03-24 16:44 ` [RFC Part1 PATCH 07/13] x86/compressed: register GHCB memory when SNP is active Brijesh Singh
2021-04-07 11:59 ` Borislav Petkov
2021-04-07 17:34 ` Brijesh Singh
2021-04-07 17:54 ` Tom Lendacky
2021-04-08 8:17 ` Borislav Petkov
2021-03-24 16:44 ` [RFC Part1 PATCH 08/13] x86/sev-es: register GHCB memory when SEV-SNP " Brijesh Singh
2021-04-08 8:38 ` Borislav Petkov
2021-03-24 16:44 ` [RFC Part1 PATCH 09/13] x86/kernel: add support to validate memory in early enc attribute change Brijesh Singh
2021-04-08 11:40 ` Borislav Petkov
2021-04-08 12:25 ` Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 10/13] X86: kernel: make the bss.decrypted section shared in RMP table Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 11/13] x86/kernel: validate rom memory before accessing when SEV-SNP is active Brijesh Singh
2021-04-09 16:53 ` Borislav Petkov
2021-04-09 17:40 ` Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 12/13] x86/sev-es: make GHCB get and put helper accessible outside Brijesh Singh
2021-03-24 16:44 ` [RFC Part1 PATCH 13/13] x86/kernel: add support to validate memory when changing C-bit Brijesh Singh
2021-04-12 11:49 ` Borislav Petkov
2021-04-12 12:55 ` Brijesh Singh
2021-04-12 13:05 ` Borislav Petkov
2021-04-12 14:31 ` Brijesh Singh
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