Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Sat, 14 Jan 2023 00:01:01 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Chao Peng <chao.p.peng@linux.intel.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        linux-doc@vger.kernel.org, qemu-devel@nongnu.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Arnd Bergmann <arnd@arndb.de>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Miaohe Lin <linmiaohe@huawei.com>, x86@kernel.org,
        "H . Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
        Steven Price <steven.price@arm.com>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
        ak@linux.intel.com, david@redhat.com, aarcange@redhat.com,
        ddutile@redhat.com, dhildenb@redhat.com,
        Quentin Perret <qperret@google.com>, tabba@google.com,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        wei.w.wang@intel.com
Subject: Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE
Message-ID: <Y8HwvTik/2avrCOU@google.com>
References: <20221202061347.1070246-1-chao.p.peng@linux.intel.com>
 <20221202061347.1070246-10-chao.p.peng@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20221202061347.1070246-10-chao.p.peng@linux.intel.com>
Precedence: bulk

On Fri, Dec 02, 2022, Chao Peng wrote:
> @@ -10357,6 +10364,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  		if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
>  			static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
> +
> +		if (kvm_check_request(KVM_REQ_MEMORY_MCE, vcpu)) {
> +			vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;

Synthesizing triple fault shutdown is not the right approach.  Even with TDX's
MCE "architecture" (heavy sarcasm), it's possible that host userspace and the
guest have a paravirt interface for handling memory errors without killing the
host.

> +			r = 0;
> +			goto out;
> +		}
>  	}


> @@ -1982,6 +2112,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
>  			mem->memory_size))
>  		return -EINVAL;
> +	if (mem->flags & KVM_MEM_PRIVATE &&
> +		(mem->restricted_offset & (PAGE_SIZE - 1) ||

Align indentation.

> +		 mem->restricted_offset > U64_MAX - mem->memory_size))

Strongly prefer to use similar logic to existing code that detects wraps:

		mem->restricted_offset + mem->memory_size < mem->restricted_offset

This is also where I'd like to add the "gfn is aligned to offset" check, though
my brain is too fried to figure that out right now.

> +		return -EINVAL;
>  	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
>  		return -EINVAL;
>  	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> @@ -2020,6 +2154,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
>  			return -EINVAL;
>  	} else { /* Modify an existing slot. */
> +		/* Private memslots are immutable, they can only be deleted. */

I'm 99% certain I suggested this, but if we're going to make these memslots
immutable, then we should straight up disallow dirty logging, otherwise we'll
end up with a bizarre uAPI.

> +		if (mem->flags & KVM_MEM_PRIVATE)
> +			return -EINVAL;
>  		if ((mem->userspace_addr != old->userspace_addr) ||
>  		    (npages != old->npages) ||
>  		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> @@ -2048,10 +2185,28 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  	new->npages = npages;
>  	new->flags = mem->flags;
>  	new->userspace_addr = mem->userspace_addr;
> +	if (mem->flags & KVM_MEM_PRIVATE) {
> +		new->restricted_file = fget(mem->restricted_fd);
> +		if (!new->restricted_file ||
> +		    !file_is_restrictedmem(new->restricted_file)) {
> +			r = -EINVAL;
> +			goto out;
> +		}
> +		new->restricted_offset = mem->restricted_offset;
> +	}
> +
> +	new->kvm = kvm;

Set this above, just so that the code flows better.