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From: Borislav Petkov <bp@alien8.de>
To: Brijesh Singh <brijesh.singh@amd.com>
Cc: 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>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	David Rientjes <rientjes@google.com>,
	Sean Christopherson <seanjc@google.com>
Subject: Re: [RFC Part1 PATCH 13/13] x86/kernel: add support to validate memory when changing C-bit
Date: Mon, 12 Apr 2021 15:05:42 +0200	[thread overview]
Message-ID: <20210412130542.GD24283@zn.tnic> (raw)
In-Reply-To: <f9a69ad8-54bb-70f1-d606-6497e5753bb0@amd.com>

On Mon, Apr 12, 2021 at 07:55:01AM -0500, Brijesh Singh wrote:
> The cur_entry is updated by the hypervisor. While building the psc
> buffer the guest sets the cur_entry=0 and the end_entry point to the
> last valid entry. The cur_entry is incremented by the hypervisor after
> it successfully processes one 4K page. As per the spec, the hypervisor
> could get interrupted in middle of the page state change and cur_entry
> allows the guest to resume the page state change from the point where it
> was interrupted.

This is non-obvious and belongs in a comment above it. Otherwise it
looks weird.

> Since we can get interrupted while executing the PSC so just to be safe
> I re-initialized the scratch scratch area with our buffer instead of
> relying on old values.

Ditto.

> As per the spec the caller must check that the cur_entry > end_entry to
> determine whether all the entries are processed. If not then retry the
> state change. The hypervisor will skip the previously processed entries.
> The snp_page_state_vmgexit() is implemented to return only after all the
> entries are changed.

Ditto.

This whole mechanism of what the guest does and what the HV does, needs
to be explained in a bigger comment somewhere around there so that it is
clear what's going on.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-04-12 13:05 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
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 [this message]
2021-04-12 14:31         ` Brijesh Singh

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