From: Vlastimil Babka <vbabka@suse.cz>
To: Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: seanjc@google.com, michael.roth@amd.com, isaku.yamahata@intel.com
Subject: Re: [PATCH 02/11] KVM: guest_memfd: Use AS_INACCESSIBLE when creating guest_memfd inode
Date: Mon, 29 Apr 2024 15:15:02 +0200 [thread overview]
Message-ID: <c9b39bd3-235e-4b04-838a-b0238ecf2295@suse.cz> (raw)
In-Reply-To: <20240404185034.3184582-3-pbonzini@redhat.com>
On 4/4/24 8:50 PM, Paolo Bonzini wrote:
> From: Michael Roth <michael.roth@amd.com>
>
> truncate_inode_pages_range() may attempt to zero pages before truncating
> them, and this will occur before arch-specific invalidations can be
> triggered via .invalidate_folio/.free_folio hooks via kvm_gmem_aops. For
> AMD SEV-SNP this would result in an RMP #PF being generated by the
> hardware, which is currently treated as fatal (and even if specifically
> allowed for, would not result in anything other than garbage being
> written to guest pages due to encryption). On Intel TDX this would also
> result in undesirable behavior.
>
> Set the AS_INACCESSIBLE flag to prevent the MM from attempting
> unexpected accesses of this sort during operations like truncation.
>
> This may also in some cases yield a decent performance improvement for
> guest_memfd userspace implementations that hole-punch ranges immediately
> after private->shared conversions via KVM_SET_MEMORY_ATTRIBUTES, since
> the current implementation of truncate_inode_pages_range() always ends
> up zero'ing an entire 4K range if it is backing by a 2M folio.
>
> Link: https://lore.kernel.org/lkml/ZR9LYhpxTaTk6PJX@google.com/
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> Message-ID: <20240329212444.395559-6-michael.roth@amd.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> virt/kvm/guest_memfd.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 0f4e0cf4f158..5a929536ecf2 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -357,6 +357,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
> inode->i_private = (void *)(unsigned long)flags;
> inode->i_op = &kvm_gmem_iops;
> inode->i_mapping->a_ops = &kvm_gmem_aops;
> + inode->i_mapping->flags |= AS_INACCESSIBLE;
> inode->i_mode |= S_IFREG;
> inode->i_size = size;
> mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
next prev parent reply other threads:[~2024-04-29 13:15 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-04 18:50 [PATCH 00/11] KVM: guest_memfd: New hooks and functionality for SEV-SNP and TDX Paolo Bonzini
2024-04-04 18:50 ` [PATCH 01/11] mm: Introduce AS_INACCESSIBLE for encrypted/confidential memory Paolo Bonzini
2024-04-29 13:14 ` Vlastimil Babka
2024-04-04 18:50 ` [PATCH 02/11] KVM: guest_memfd: Use AS_INACCESSIBLE when creating guest_memfd inode Paolo Bonzini
2024-04-29 13:15 ` Vlastimil Babka [this message]
2024-04-04 18:50 ` [PATCH 03/11] KVM: guest_memfd: pass error up from filemap_grab_folio Paolo Bonzini
2024-04-04 18:50 ` [PATCH 04/11] filemap: add FGP_CREAT_ONLY Paolo Bonzini
2024-04-25 5:52 ` Paolo Bonzini
2024-04-29 13:26 ` Vlastimil Babka
2024-04-04 18:50 ` [PATCH 05/11] KVM: guest_memfd: limit overzealous WARN Paolo Bonzini
2024-04-04 18:50 ` [PATCH 06/11] KVM: guest_memfd: Add hook for initializing memory Paolo Bonzini
2024-04-22 10:53 ` Xu Yilun
2024-05-07 16:17 ` Paolo Bonzini
2024-04-04 18:50 ` [PATCH 07/11] KVM: guest_memfd: extract __kvm_gmem_get_pfn() Paolo Bonzini
2024-04-09 23:35 ` Michael Roth
2024-04-24 22:34 ` Sean Christopherson
2024-04-24 22:59 ` Sean Christopherson
2024-04-04 18:50 ` [PATCH 08/11] KVM: guest_memfd: extract __kvm_gmem_punch_hole() Paolo Bonzini
2024-04-04 18:50 ` [PATCH 09/11] KVM: guest_memfd: Add interface for populating gmem pages with user data Paolo Bonzini
2024-04-22 14:44 ` Xu Yilun
2024-04-23 23:50 ` Isaku Yamahata
2024-04-24 22:24 ` Sean Christopherson
2024-04-25 1:12 ` Isaku Yamahata
2024-04-25 6:01 ` Paolo Bonzini
2024-04-25 16:00 ` Sean Christopherson
2024-04-25 16:51 ` Isaku Yamahata
2024-04-26 5:44 ` Paolo Bonzini
2024-04-26 17:15 ` Isaku Yamahata
2024-04-26 5:41 ` Paolo Bonzini
2024-04-26 15:17 ` Sean Christopherson
2024-04-24 22:32 ` Sean Christopherson
2024-04-25 5:56 ` Paolo Bonzini
2024-04-04 18:50 ` [PATCH 10/11] KVM: guest_memfd: Add hook for invalidating memory Paolo Bonzini
2024-04-04 18:50 ` [PATCH 11/11] KVM: x86: Add gmem hook for determining max NPT mapping level Paolo Bonzini
2024-04-09 23:46 ` Michael Roth
2024-04-19 18:26 ` Isaku Yamahata
2024-04-22 14:52 ` Xu Yilun
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