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From: Peter Zijlstra <peterz@infradead.org>
To: Brijesh Singh <brijesh.singh@amd.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, tglx@linutronix.de, bp@alien8.de,
	jroedel@suse.de, thomas.lendacky@amd.com, pbonzini@redhat.com,
	mingo@redhat.com, dave.hansen@intel.com, rientjes@google.com,
	seanjc@google.com, hpa@zytor.com, tony.luck@intel.com
Subject: Re: [PATCH Part2 RFC v2 08/37] x86/sev: Split the physmap when adding the page in RMP table
Date: Mon, 3 May 2021 17:07:15 +0200	[thread overview]
Message-ID: <YJARo9vpAgb6VmLI@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210430123822.13825-9-brijesh.singh@amd.com>

On Fri, Apr 30, 2021 at 07:37:53AM -0500, Brijesh Singh wrote:

> This poses a challenge in the Linux memory model. The Linux kernel
> creates a direct mapping of all the physical memory -- referred to as
> the physmap. The physmap may contain a valid mapping of guest owned pages.
> During the page table walk, the host access may get into the situation where
> one of the pages within the large page is owned by the guest (i.e assigned
> bit is set in RMP). A write to a non-guest within the large page will
> raise an RMP violation. To workaround it, call set_memory_4k() to split
> the physmap before adding the page in the RMP table. This ensures that the
> pages added in the RMP table are used as 4K in the physmap.

What's an RMP violation and why are they a problem?

> The spliting of the physmap is a temporary solution until the kernel page
> fault handler is improved to split the kernel address on demand.

How is that an improvement? Fracturing the physmap sucks whichever way
around.

> One of the
> disadvtange of splitting is that eventually, it will end up breaking down
> the entire physmap unless its coalesce back to a large page. I am open to
> the suggestation on various approaches we could take to address this problem.

Have the hardware fracture the TLB entry internally?

  reply	other threads:[~2021-05-03 15:07 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-30 12:37 [PATCH Part2 RFC v2 00/37] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 01/37] KVM: SVM: Add support to handle AP reset MSR protocol Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 02/37] KVM: SVM: Provide the Hypervisor Feature support VMGEXIT Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 03/37] KVM: SVM: Increase the GHCB protocol version Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 04/37] x86/cpufeatures: Add SEV-SNP CPU feature Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 05/37] x86/sev: Add the host SEV-SNP initialization support Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 06/37] x86/sev: Add RMP entry lookup helpers Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 07/37] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 08/37] x86/sev: Split the physmap when adding the page in RMP table Brijesh Singh
2021-05-03 15:07   ` Peter Zijlstra [this message]
2021-05-03 15:15   ` Andy Lutomirski
2021-05-03 15:41     ` Dave Hansen
2021-05-07 11:28       ` Vlastimil Babka
2021-04-30 12:37 ` [PATCH Part2 RFC v2 09/37] x86/traps: Define RMP violation #PF error code Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 10/37] x86/fault: Add support to handle the RMP fault for kernel address Brijesh Singh
2021-05-03 14:44   ` Dave Hansen
2021-05-03 15:03     ` Andy Lutomirski
2021-05-03 15:49       ` Brijesh Singh
2021-05-03 15:37     ` Brijesh Singh
2021-05-03 16:15       ` Dave Hansen
2021-05-03 17:19         ` Brijesh Singh
2021-05-03 17:31           ` Brijesh Singh
2021-05-03 17:40           ` Andy Lutomirski
2021-05-03 19:41             ` Brijesh Singh
2021-05-03 19:43               ` Dave Hansen
2021-05-04 12:31                 ` Brijesh Singh
2021-05-04 14:33                   ` Dave Hansen
2021-05-04 15:16                     ` Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 11/37] x86/fault: Add support to handle the RMP fault for user address Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 12/37] crypto:ccp: Define the SEV-SNP commands Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 13/37] crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 14/37] crypto: ccp: Shutdown SNP firmware on kexec Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 15/37] crypto:ccp: Provide APIs to issue SEV-SNP commands Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 16/37] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled Brijesh Singh
2021-05-10 18:23   ` Peter Gonda
2021-05-10 20:07     ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 17/37] crypto: ccp: Handle the legacy SEV command " Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 18/37] KVM: SVM: make AVIC backing, VMSA and VMCB memory allocation SNP safe Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 19/37] KVM: SVM: Add initial SEV-SNP support Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 20/37] KVM: SVM: define new SEV_FEATURES field in the VMCB Save State Area Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 21/37] KVM: SVM: Add KVM_SNP_INIT command Brijesh Singh
2021-05-06 20:25   ` Peter Gonda
2021-05-06 22:29     ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 22/37] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 23/37] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_UPDATE command Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 24/37] KVM: SVM: Reclaim the guest pages when SEV-SNP VM terminates Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 25/37] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 26/37] KVM: X86: Add kvm_x86_ops to get the max page level for the TDP Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 27/37] KVM: X86: Introduce kvm_mmu_map_tdp_page() for use by SEV Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 28/37] KVM: X86: Introduce kvm_mmu_get_tdp_walk() for SEV-SNP use Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 29/37] KVM: X86: Define new RMP check related #NPF error bits Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 30/37] KVM: X86: update page-fault trace to log the 64-bit error code Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 31/37] KVM: SVM: Add support to handle GHCB GPA register VMGEXIT Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 32/37] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT Brijesh Singh
2021-05-10 17:30   ` Peter Gonda
2021-05-10 17:51     ` Brijesh Singh
2021-05-10 19:59       ` Peter Gonda
2021-05-10 20:50         ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 33/37] KVM: SVM: Add support to handle " Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 34/37] KVM: X86: Export the kvm_zap_gfn_range() for the SNP use Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 35/37] KVM: SVM: Add support to handle the RMP nested page fault Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 36/37] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event Brijesh Singh
2021-05-10 18:57   ` Peter Gonda
2021-05-10 20:14     ` Brijesh Singh
2021-05-10 21:17       ` Sean Christopherson
2021-05-11 18:34         ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 37/37] KVM: SVM: Advertise the SEV-SNP feature support Brijesh Singh

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