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From: Sean Christopherson <seanjc@google.com>
To: Brijesh Singh <brijesh.singh@amd.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-efi@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev,
	linux-mm@kvack.org, linux-crypto@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Dov Murik <dovmurik@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	tony.luck@intel.com, npmccallum@redhat.com,
	brijesh.ksingh@gmail.com
Subject: Re: [PATCH Part2 RFC v4 35/40] KVM: Add arch hooks to track the host write to guest memory
Date: Mon, 19 Jul 2021 23:30:26 +0000	[thread overview]
Message-ID: <YPYLEksyzOWHZwpA@google.com> (raw)
In-Reply-To: <20210707183616.5620-36-brijesh.singh@amd.com>

On Wed, Jul 07, 2021, Brijesh Singh wrote:
> The kvm_write_guest{_page} and kvm_vcpu_write_guest{_page} are used by
> the hypevisor to write to the guest memory. The kvm_vcpu_map() and
> kvm_map_gfn() are used by the hypervisor to map the guest memory and
> and access it later.
> 
> When SEV-SNP is enabled in the guest VM, the guest memory pages can
> either be a private or shared. A write from the hypervisor goes through
> the RMP checks. If hardware sees that hypervisor is attempting to write
> to a guest private page, then it triggers an RMP violation (i.e, #PF with
> RMP bit set).
> 
> Enhance the KVM guest write helpers to invoke an architecture specific
> hooks (kvm_arch_write_gfn_{begin,end}) to track the write access from the
> hypervisor.
> 
> When SEV-SNP is enabled, the guest uses the PAGE_STATE vmgexit to ask the
> hypervisor to change the page state from shared to private or vice versa.
> While changing the page state to private, use the
> kvm_host_write_track_is_active() to check whether the page is being
> tracked for the host write access (i.e either mapped or kvm_write_guest
> is in progress). If its tracked, then do not change the page state.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---

...

> @@ -3468,3 +3489,33 @@ int sev_get_tdp_max_page_level(struct kvm_vcpu *vcpu, gpa_t gpa, int max_level)
>  
>  	return min_t(uint32_t, level, max_level);
>  }
> +
> +void sev_snp_write_page_begin(struct kvm *kvm, struct kvm_memory_slot *slot, gfn_t gfn)
> +{
> +	struct rmpentry *e;
> +	int level, rc;
> +	kvm_pfn_t pfn;
> +
> +	if (!sev_snp_guest(kvm))
> +		return;
> +
> +	pfn = gfn_to_pfn(kvm, gfn);
> +	if (is_error_noslot_pfn(pfn))
> +		return;
> +
> +	e = snp_lookup_page_in_rmptable(pfn_to_page(pfn), &level);
> +	if (unlikely(!e))
> +		return;
> +
> +	/*
> +	 * A hypervisor should never write to the guest private page. A write to the
> +	 * guest private will cause an RMP violation. If the guest page is private,
> +	 * then make it shared.

NAK on converting RMP entries in response to guest accesses.  Corrupting guest
data (due to dropping the "validated" flag) on a rogue/incorrect guest emulation
request or misconfigured PV feature is double ungood.  The potential kernel panic
below isn't much better.

And I also don't think we need this heavyweight flow for user access, e.g.
__copy_to_user(), just eat the RMP violation #PF like all other #PFs and exit
to userspace with -EFAULT.

kvm_vcpu_map() and friends might need the manual lookup, at least initially, but
in an ideal world that would be naturally handled by gup(), e.g. by unmapping
guest private memory or whatever approach TDX ends up employing to avoid #MCs.

> +	 */
> +	if (rmpentry_assigned(e)) {
> +		pr_err("SEV-SNP: write to guest private gfn %llx\n", gfn);
> +		rc = snp_make_page_shared(kvm_get_vcpu(kvm, 0),
> +				gfn << PAGE_SHIFT, pfn, PG_LEVEL_4K);
> +		BUG_ON(rc != 0);
> +	}
> +}

...

> +void kvm_arch_write_gfn_begin(struct kvm *kvm, struct kvm_memory_slot *slot, gfn_t gfn)
> +{
> +	update_gfn_track(slot, gfn, KVM_PAGE_TRACK_WRITE, 1);

Tracking only writes isn't correct, as KVM reads to guest private memory will
return garbage.  Pulling the rug out from under KVM reads won't fail as
spectacularly as writes (at least not right away), but they'll still fail.  I'm
actually ok reading garbage if the guest screws up, but KVM needs consistent
semantics.

Good news is that per-gfn tracking is probably overkill anyways.  As mentioned
above, user access don't need extra magic, they either fail or they don't.

For kvm_vcpu_map(), one thought would be to add a "short-term" map variant that
is not allowed to be retained across VM-Entry, and then use e.g. SRCU to block
PSC requests until there are no consumers.

> +	if (kvm_x86_ops.write_page_begin)
> +		kvm_x86_ops.write_page_begin(kvm, slot, gfn);
> +}

  reply	other threads:[~2021-07-19 23:30 UTC|newest]

Thread overview: 176+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-07 18:35 [PATCH Part2 RFC v4 00/40] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 01/40] KVM: SVM: Add support to handle AP reset MSR protocol Brijesh Singh
2021-07-14 20:17   ` Sean Christopherson
2021-07-15  7:39     ` Joerg Roedel
2021-07-15 13:42     ` Tom Lendacky
2021-07-15 15:45       ` Sean Christopherson
2021-07-15 17:05         ` Tom Lendacky
2021-07-07 18:35 ` [PATCH Part2 RFC v4 02/40] KVM: SVM: Provide the Hypervisor Feature support VMGEXIT Brijesh Singh
2021-07-14 20:37   ` Sean Christopherson
2021-07-14 21:00     ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 03/40] x86/cpufeatures: Add SEV-SNP CPU feature Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 04/40] x86/sev: Add the host SEV-SNP initialization support Brijesh Singh
2021-07-14 21:07   ` Sean Christopherson
2021-07-14 22:02     ` Brijesh Singh
2021-07-14 22:06       ` Sean Christopherson
2021-07-14 22:11         ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 05/40] x86/sev: Add RMP entry lookup helpers Brijesh Singh
2021-07-15 18:37   ` Sean Christopherson
2021-07-15 19:28     ` Brijesh Singh
2021-07-16 17:22       ` Brijesh Singh
2021-07-20 22:06         ` Sean Christopherson
2021-07-20 23:10           ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 06/40] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction Brijesh Singh
2021-07-12 18:44   ` Peter Gonda
2021-07-12 19:00     ` Dave Hansen
2021-07-15 18:56       ` Sean Christopherson
2021-07-15 19:08         ` Dave Hansen
2021-07-15 19:18           ` Sean Christopherson
2021-07-07 18:35 ` [PATCH Part2 RFC v4 07/40] x86/sev: Split the physmap when adding the page in RMP table Brijesh Singh
2021-07-14 22:25   ` Sean Christopherson
2021-07-15 17:05     ` Brijesh Singh
2021-07-15 17:51       ` Sean Christopherson
2021-07-15 18:14         ` Brijesh Singh
2021-07-15 18:39           ` Sean Christopherson
2021-07-15 19:38             ` Brijesh Singh
2021-07-15 22:01               ` Sean Christopherson
2021-07-15 22:11                 ` Brijesh Singh
2021-07-30 11:31               ` Vlastimil Babka
2021-07-30 16:10                 ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 08/40] x86/traps: Define RMP violation #PF error code Brijesh Singh
2021-07-15 19:02   ` Sean Christopherson
2021-07-15 19:16     ` Dave Hansen
2021-07-07 18:35 ` [PATCH Part2 RFC v4 09/40] x86/fault: Add support to dump RMP entry on fault Brijesh Singh
2021-07-07 19:21   ` Dave Hansen
2021-07-08 15:02     ` Brijesh Singh
2021-07-08 15:30       ` Dave Hansen
2021-07-08 16:48         ` Brijesh Singh
2021-07-08 16:58           ` Dave Hansen
2021-07-08 17:11             ` Brijesh Singh
2021-07-08 17:15               ` Dave Hansen
2021-07-07 18:35 ` [PATCH Part2 RFC v4 10/40] x86/fault: Add support to handle the RMP fault for user address Brijesh Singh
2021-07-08 16:16   ` Dave Hansen
2021-07-12 15:43     ` Brijesh Singh
2021-07-12 16:00       ` Dave Hansen
2021-07-12 16:11         ` Brijesh Singh
2021-07-12 16:15           ` Dave Hansen
2021-07-12 16:24             ` Brijesh Singh
2021-07-12 16:29               ` Dave Hansen
2021-07-12 16:49                 ` Brijesh Singh
2021-07-15 21:53                   ` Sean Christopherson
2021-07-30 16:00   ` Vlastimil Babka
2021-07-30 16:31     ` Dave Hansen
2021-07-07 18:35 ` [PATCH Part2 RFC v4 11/40] crypto:ccp: Define the SEV-SNP commands Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 12/40] crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 13/40] crypto: ccp: Shutdown SNP firmware on kexec Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 14/40] crypto:ccp: Provide APIs to issue SEV-SNP commands Brijesh Singh
2021-07-08 18:56   ` Dr. David Alan Gilbert
2021-07-07 18:35 ` [PATCH Part2 RFC v4 15/40] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled Brijesh Singh
2021-07-14 13:22   ` Marc Orr
2021-07-14 16:45     ` Brijesh Singh
2021-07-14 18:14       ` Marc Orr
2021-07-15 23:48   ` Sean Christopherson
2021-07-16 12:55     ` Brijesh Singh
2021-07-16 15:35       ` Sean Christopherson
2021-07-16 15:47         ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 16/40] crypto: ccp: Handle the legacy SEV command " Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 17/40] crypto: ccp: Add the SNP_PLATFORM_STATUS command Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 18/40] crypto: ccp: Add the SNP_{SET,GET}_EXT_CONFIG command Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 19/40] crypto: ccp: provide APIs to query extended attestation report Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 20/40] KVM: SVM: Make AVIC backing, VMSA and VMCB memory allocation SNP safe Brijesh Singh
2021-07-14 13:35   ` Marc Orr
2021-07-14 16:47     ` Brijesh Singh
2021-07-20 18:02   ` Sean Christopherson
2021-08-03 14:38     ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 21/40] KVM: SVM: Add initial SEV-SNP support Brijesh Singh
2021-07-16 18:00   ` Sean Christopherson
2021-07-16 18:46     ` Brijesh Singh
2021-07-16 19:31       ` Sean Christopherson
2021-07-16 21:03         ` Brijesh Singh
2021-07-07 18:35 ` [PATCH Part2 RFC v4 22/40] KVM: SVM: Add KVM_SNP_INIT command Brijesh Singh
2021-07-16 19:33   ` Sean Christopherson
2021-07-16 21:25     ` Brijesh Singh
2021-07-19 20:24       ` Sean Christopherson
2021-07-07 18:35 ` [PATCH Part2 RFC v4 23/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command Brijesh Singh
2021-07-12 18:45   ` Peter Gonda
2021-07-16 19:43   ` Sean Christopherson
2021-07-16 21:42     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 24/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_UPDATE command Brijesh Singh
2021-07-16 20:01   ` Sean Christopherson
2021-07-16 22:00     ` Brijesh Singh
2021-07-19 20:51       ` Sean Christopherson
2021-07-19 21:34         ` Brijesh Singh
2021-07-19 21:36           ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 25/40] KVM: SVM: Reclaim the guest pages when SEV-SNP VM terminates Brijesh Singh
2021-07-16 20:09   ` Sean Christopherson
2021-07-16 22:16     ` Brijesh Singh
2021-07-17  0:46       ` Sean Christopherson
2021-07-19 12:55         ` Brijesh Singh
2021-07-19 17:18           ` Sean Christopherson
2021-07-19 18:34             ` Brijesh Singh
2021-07-19 19:03               ` Sean Christopherson
2021-07-19 19:14                 ` Sean Christopherson
2021-07-19 19:37                 ` Brijesh Singh
2021-07-20 16:40                   ` Sean Christopherson
2021-07-20 18:23                     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 26/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command Brijesh Singh
2021-07-16 20:18   ` Sean Christopherson
2021-07-16 22:48     ` Brijesh Singh
2021-07-19 16:54       ` Sean Christopherson
2021-07-19 18:29         ` Brijesh Singh
2021-07-19 19:14           ` Sean Christopherson
2021-07-19 19:49             ` Brijesh Singh
2021-07-19 20:13               ` Sean Christopherson
2021-07-21 17:53         ` Marc Orr
2021-07-07 18:36 ` [PATCH Part2 RFC v4 27/40] KVM: X86: Add kvm_x86_ops to get the max page level for the TDP Brijesh Singh
2021-07-16 19:19   ` Sean Christopherson
2021-07-16 20:41     ` Brijesh Singh
2021-07-20 19:38       ` Sean Christopherson
2021-07-20 20:06         ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 28/40] KVM: X86: Introduce kvm_mmu_map_tdp_page() for use by SEV Brijesh Singh
2021-07-16 18:15   ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 29/40] KVM: X86: Introduce kvm_mmu_get_tdp_walk() for SEV-SNP use Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 30/40] KVM: X86: Define new RMP check related #NPF error bits Brijesh Singh
2021-07-16 20:22   ` Sean Christopherson
2021-07-17  0:34     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 31/40] KVM: X86: update page-fault trace to log the 64-bit error code Brijesh Singh
2021-07-16 20:25   ` Sean Christopherson
2021-07-17  0:35     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 32/40] KVM: SVM: Add support to handle GHCB GPA register VMGEXIT Brijesh Singh
2021-07-16 20:45   ` Sean Christopherson
2021-07-17  0:44     ` Brijesh Singh
2021-07-19 20:04       ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 33/40] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT Brijesh Singh
2021-07-16 21:00   ` Sean Christopherson
2021-07-19 14:19     ` Brijesh Singh
2021-07-19 18:55       ` Sean Christopherson
2021-07-19 19:15         ` Brijesh Singh
2021-08-13 16:32         ` Borislav Petkov
2021-07-07 18:36 ` [PATCH Part2 RFC v4 34/40] KVM: SVM: Add support to handle " Brijesh Singh
2021-07-16 21:14   ` Sean Christopherson
2021-07-19 14:24     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 35/40] KVM: Add arch hooks to track the host write to guest memory Brijesh Singh
2021-07-19 23:30   ` Sean Christopherson [this message]
2021-07-20 15:15     ` Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 36/40] KVM: X86: Export the kvm_zap_gfn_range() for the SNP use Brijesh Singh
2021-07-07 18:36 ` [PATCH Part2 RFC v4 37/40] KVM: SVM: Add support to handle the RMP nested page fault Brijesh Singh
2021-07-20  0:10   ` Sean Christopherson
2021-07-20 17:55     ` Brijesh Singh
2021-07-20 22:31       ` Sean Christopherson
2021-07-20 23:53         ` Brijesh Singh
2021-07-21 20:15           ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 38/40] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event Brijesh Singh
2021-07-19 22:50   ` Sean Christopherson
2021-07-20 14:37     ` Brijesh Singh
2021-07-20 16:28       ` Sean Christopherson
2021-07-20 18:21         ` Brijesh Singh
2021-07-20 22:09           ` Sean Christopherson
2021-07-07 18:36 ` [PATCH Part2 RFC v4 39/40] KVM: SVM: Use a VMSA physical address variable for populating VMCB Brijesh Singh
2021-07-21  0:20   ` Sean Christopherson
2021-07-21 16:26     ` Tom Lendacky
2021-07-07 18:36 ` [PATCH Part2 RFC v4 40/40] KVM: SVM: Support SEV-SNP AP Creation NAE event Brijesh Singh
2021-07-21  0:01   ` Sean Christopherson
2021-07-21 17:47     ` Tom Lendacky
2021-07-21 19:52       ` Sean Christopherson
2021-08-20 14:44         ` Tom Lendacky
2021-07-08 15:40 ` [PATCH Part2 RFC v4 00/40] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Dave Hansen

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