linux-kernel - Re: [PATCH v8 08/30] KVM: selftests: TDX: Update load_td_memory_region() for VM memory backed by guest memfd

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Message-ID: <bec79c4a-499d-4f82-bfea-05746d4085e9@intel.com>
Date: Wed, 13 Aug 2025 07:42:33 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>, Sean Christopherson
	<seanjc@...gle.com>, Sagi Shahar <sagis@...gle.com>
CC: <linux-kselftest@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
	Shuah Khan <shuah@...nel.org>, Ackerley Tng <ackerleytng@...gle.com>, "Ryan
 Afranji" <afranji@...gle.com>, Andrew Jones <ajones@...tanamicro.com>, "Isaku
 Yamahata" <isaku.yamahata@...el.com>, Erdem Aktas <erdemaktas@...gle.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Roger Wang
	<runanwang@...gle.com>, Oliver Upton <oliver.upton@...ux.dev>, "Pratik R.
 Sampat" <pratikrajesh.sampat@....com>, Ira Weiny <ira.weiny@...el.com>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH v8 08/30] KVM: selftests: TDX: Update
 load_td_memory_region() for VM memory backed by guest memfd

Hi Binbin,

On 8/13/25 2:23 AM, Binbin Wu wrote:
> 
> 
> On 8/12/2025 4:31 AM, Sean Christopherson wrote:
>> On Thu, Aug 07, 2025, Sagi Shahar wrote:
> [...]
>>> +
>>>   /*
>>>    * TD creation/setup/finalization
>>>    */
>>> @@ -459,28 +474,35 @@ static void load_td_memory_region(struct kvm_vm *vm,
>>>       if (!sparsebit_any_set(pages))
>>>           return;
>>>   +    if (region->region.guest_memfd != -1)
>>> +        register_encrypted_memory_region(vm, region);
>>> +
>>>       sparsebit_for_each_set_range(pages, i, j) {
>>>           const uint64_t size_to_load = (j - i + 1) * vm->page_size;
>>>           const uint64_t offset =
>>>               (i - lowest_page_in_region) * vm->page_size;
>>>           const uint64_t hva = hva_base + offset;
>>>           const uint64_t gpa = gpa_base + offset;
>>> -        void *source_addr;
>>> +        void *source_addr = (void *)hva;
>>>             /*
>>>            * KVM_TDX_INIT_MEM_REGION ioctl cannot encrypt memory in place.
>>>            * Make a copy if there's only one backing memory source.
>>>            */
>>> -        source_addr = mmap(NULL, size_to_load, PROT_READ | PROT_WRITE,
>>> -                   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>>> -        TEST_ASSERT(source_addr,
>>> -                "Could not allocate memory for loading memory region");
>>> -
>>> -        memcpy(source_addr, (void *)hva, size_to_load);
>>> +        if (region->region.guest_memfd == -1) {
>> Oh, here's the "if".
> 
> Is it still possible for "region->region.guest_memfd == -1" case?
> KVM_TDX_INIT_MEM_REGION can only work with guest memfd, right?
> 
This is still used and supports test "KVM: selftests: TDX: Test
LOG_DIRTY_PAGES flag to a non-GUEST_MEMFD memslot" found in patch #30 that
was created to support the issue encountered when QEMU attaches an emulated
VGA device to a TD. More details available in the fix:
fbb4adadea55 ("KVM: x86: Make cpu_dirty_log_size a per-VM value")

Reinette