linux-kernel - Re: [PATCH v10 046/108] KVM: Add flags to struct kvm_gfn

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Date:   Wed, 14 Dec 2022 10:51:31 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v10 046/108] KVM: Add flags to struct kvm_gfn_range

On Sat, 2022-10-29 at 23:22 -0700, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> kvm_unmap_gfn_range() needs to know the reason of the callback for TDX.
> mmu notifier, set memattr ioctl or restrictedmem notifier.  Based on the
> reason, TDX changes the behavior.  For mmu notifier, it's the operation on
> shared memory slot to zap shared PTE.  For set memattr, private<->shared
> conversion, zap the original PTE.  For restrictedmem, it's a hint that TDX
> can ignore.

Could you elaborate why restricted memfd notifier can be ignored? IIUC if
userspace punch a hole, the pages within the hole will be de-allocated.  So why
can such notifier be ignored?

Btw, I think this patch should be just merged to the patch which consumes those
flags (checked it is next patch).  It's easier to review when putting them
together.

> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  include/linux/kvm_host.h | 8 +++++++-
>  virt/kvm/kvm_main.c      | 5 ++++-
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 839d98d56632..b658803ea2c7 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -247,12 +247,18 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
>  
>  
>  #if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_HAVE_KVM_RESTRICTED_MEM)
> +#define KVM_GFN_RANGE_FLAGS_RESTRICTED_MEM	BIT(0)
> +#define KVM_GFN_RANGE_FLAGS_SET_MEM_ATTR	BIT(1)
>  struct kvm_gfn_range {
>  	struct kvm_memory_slot *slot;
>  	gfn_t start;
>  	gfn_t end;
> -	pte_t pte;
> +	union {
> +		pte_t pte;
> +		int attr;
> +	};

attribute is u64 in Chao's series.

>  	bool may_block;
> +	unsigned int flags;
>  };