Message-ID: <aDU3pN/0FVbowmNH@yzhao56-desk.sh.intel.com>
Date: Tue, 27 May 2025 11:55:16 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Ackerley Tng <ackerleytng@...gle.com>
CC: <kvm@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<linux-fsdevel@...r.kernel.org>, <aik@....com>, <ajones@...tanamicro.com>,
	<akpm@...ux-foundation.org>, <amoorthy@...gle.com>,
	<anthony.yznaga@...cle.com>, <anup@...infault.org>, <aou@...s.berkeley.edu>,
	<bfoster@...hat.com>, <binbin.wu@...ux.intel.com>, <brauner@...nel.org>,
	<catalin.marinas@....com>, <chao.p.peng@...el.com>, <chenhuacai@...nel.org>,
	<dave.hansen@...el.com>, <david@...hat.com>, <dmatlack@...gle.com>,
	<dwmw@...zon.co.uk>, <erdemaktas@...gle.com>, <fan.du@...el.com>,
	<fvdl@...gle.com>, <graf@...zon.com>, <haibo1.xu@...el.com>,
	<hch@...radead.org>, <hughd@...gle.com>, <ira.weiny@...el.com>,
	<isaku.yamahata@...el.com>, <jack@...e.cz>, <james.morse@....com>,
	<jarkko@...nel.org>, <jgg@...pe.ca>, <jgowans@...zon.com>,
	<jhubbard@...dia.com>, <jroedel@...e.de>, <jthoughton@...gle.com>,
	<jun.miao@...el.com>, <kai.huang@...el.com>, <keirf@...gle.com>,
	<kent.overstreet@...ux.dev>, <kirill.shutemov@...el.com>,
	<liam.merwick@...cle.com>, <maciej.wieczor-retman@...el.com>,
	<mail@...iej.szmigiero.name>, <maz@...nel.org>, <mic@...ikod.net>,
	<michael.roth@....com>, <mpe@...erman.id.au>, <muchun.song@...ux.dev>,
	<nikunj@....com>, <nsaenz@...zon.es>, <oliver.upton@...ux.dev>,
	<palmer@...belt.com>, <pankaj.gupta@....com>, <paul.walmsley@...ive.com>,
	<pbonzini@...hat.com>, <pdurrant@...zon.co.uk>, <peterx@...hat.com>,
	<pgonda@...gle.com>, <pvorel@...e.cz>, <qperret@...gle.com>,
	<quic_cvanscha@...cinc.com>, <quic_eberman@...cinc.com>,
	<quic_mnalajal@...cinc.com>, <quic_pderrin@...cinc.com>,
	<quic_pheragu@...cinc.com>, <quic_svaddagi@...cinc.com>,
	<quic_tsoni@...cinc.com>, <richard.weiyang@...il.com>,
	<rick.p.edgecombe@...el.com>, <rientjes@...gle.com>, <roypat@...zon.co.uk>,
	<rppt@...nel.org>, <seanjc@...gle.com>, <shuah@...nel.org>,
	<steven.price@....com>, <steven.sistare@...cle.com>,
	<suzuki.poulose@....com>, <tabba@...gle.com>, <thomas.lendacky@....com>,
	<usama.arif@...edance.com>, <vannapurve@...gle.com>, <vbabka@...e.cz>,
	<viro@...iv.linux.org.uk>, <vkuznets@...hat.com>, <wei.w.wang@...el.com>,
	<will@...nel.org>, <willy@...radead.org>, <xiaoyao.li@...el.com>,
	<yilun.xu@...el.com>, <yuzenghui@...wei.com>, <zhiquan1.li@...el.com>
Subject: Re: [RFC PATCH v2 06/51] KVM: Query guest_memfd for private/shared
 status

On Wed, May 14, 2025 at 04:41:45PM -0700, Ackerley Tng wrote:
> Query guest_memfd for private/shared status if those guest_memfds
> track private/shared status.
> 
> With this patch, Coco VMs can use guest_memfd for both shared and
> private memory. If Coco VMs choose to use guest_memfd for both
> shared and private memory, by creating guest_memfd with the
> GUEST_MEMFD_FLAG_SUPPORT_SHARED flag, guest_memfd will be used to
> provide the private/shared status of the memory, instead of
> kvm->mem_attr_array.
> 
> Change-Id: I8f23d7995c12242aa4e09ccf5ec19360e9c9ed83
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> ---
>  include/linux/kvm_host.h | 19 ++++++++++++-------
>  virt/kvm/guest_memfd.c   | 22 ++++++++++++++++++++++
>  2 files changed, 34 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index b317392453a5..91279e05e010 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2508,12 +2508,22 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
>  }
>  
>  #ifdef CONFIG_KVM_GMEM_SHARED_MEM
> +
>  bool kvm_gmem_memslot_supports_shared(const struct kvm_memory_slot *slot);
> +bool kvm_gmem_is_private(struct kvm_memory_slot *slot, gfn_t gfn);
> +
>  #else
> +
>  static inline bool kvm_gmem_memslot_supports_shared(const struct kvm_memory_slot *slot)
>  {
>  	return false;
>  }
> +
> +static inline bool kvm_gmem_is_private(struct kvm_memory_slot *slot, gfn_t gfn)
> +{
> +	return false;
> +}
> +
>  #endif /* CONFIG_KVM_GMEM_SHARED_MEM */
>  
>  #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> @@ -2544,13 +2554,8 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
>  		return false;
>  
>  	slot = gfn_to_memslot(kvm, gfn);
> -	if (kvm_slot_has_gmem(slot) && kvm_gmem_memslot_supports_shared(slot)) {
> -		/*
> -		 * For now, memslots only support in-place shared memory if the
> -		 * host is allowed to mmap memory (i.e., non-Coco VMs).
> -		 */
> -		return false;
> -	}
> +	if (kvm_slot_has_gmem(slot) && kvm_gmem_memslot_supports_shared(slot))
> +		return kvm_gmem_is_private(slot, gfn);
When userspace gets an exit reason KVM_EXIT_MEMORY_FAULT, looks it needs to
update both KVM memory attribute and gmem shareability, via two separate ioctls?


>  	return kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE;

>  }
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 6f6c4d298f8f..853e989bdcb2 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -865,6 +865,28 @@ bool kvm_gmem_memslot_supports_shared(const struct kvm_memory_slot *slot)
>  }
>  EXPORT_SYMBOL_GPL(kvm_gmem_memslot_supports_shared);
>  
> +bool kvm_gmem_is_private(struct kvm_memory_slot *slot, gfn_t gfn)
> +{
> +	struct inode *inode;
> +	struct file *file;
> +	pgoff_t index;
> +	bool ret;
> +
> +	file = kvm_gmem_get_file(slot);
> +	if (!file)
> +		return false;
> +
> +	index = kvm_gmem_get_index(slot, gfn);
> +	inode = file_inode(file);
> +
> +	filemap_invalidate_lock_shared(inode->i_mapping);
> +	ret = kvm_gmem_shareability_get(inode, index) == SHAREABILITY_GUEST;
> +	filemap_invalidate_unlock_shared(inode->i_mapping);
> +
> +	fput(file);
> +	return ret;
> +}
> +
>  #else
>  #define kvm_gmem_mmap NULL
>  #endif /* CONFIG_KVM_GMEM_SHARED_MEM */
> -- 
> 2.49.0.1045.g170613ef41-goog
> 

Powered by blists - more mailing lists