Re: [PATCH v19 058/130] KVM: x86/mmu: Add a private pointer to struct kvm_mmu_page

Binbin Wu
2024-03-28T03:17:51Z

On 3/28/2024 8:02 AM, Isaku Yamahata wrote:
> On Wed, Mar 27, 2024 at 09:49:14PM +0800,
> Binbin Wu <binbin.wu@linux.intel.com> wrote:
>
>>
>> On 3/15/2024 9:09 AM, Isaku Yamahata wrote:
>>> Here is the updated one. Renamed dummy -> mirroed.
>>>
>>> When KVM resolves the KVM page fault, it walks the page tables. To reuse
>>> the existing KVM MMU code and mitigate the heavy cost of directly walking
>>> the private page table, allocate one more page to copy the mirrored page
>> Here "copy" is a bit confusing for me.
>> The mirrored page table is maintained by KVM, not copied from anywhere.
> How about, "maintain" or "keep"?

Or just use "for"?

i.e, allocate one more page for the mirrored page table ...

>
>>> table for the KVM MMU code to directly walk. Resolve the KVM page fault
>>> with the existing code, and do additional operations necessary for the
>>> private page table. To distinguish such cases, the existing KVM page table
>>> is called a shared page table (i.e., not associated with a private page
>>> table), and the page table with a private page table is called a mirrored
>>> page table. The relationship is depicted below.
>>>
>>>
>>> KVM page fault |
>>> | |
>>> V |
>>> -------------+---------- |
>>> | | |
>>> V V |
>>> shared GPA private GPA |
>>> | | |
>>> V V |
>>> shared PT root mirrored PT root | private PT root
>>> | | | |
>>> V V | V
>>> shared PT mirrored PT ----propagate----> private PT
>>> | | | |
>>> | \-----------------+------\ |
>>> | | | |
>>> V | V V
>>> shared guest page | private guest page
>>> |
>>> non-encrypted memory | encrypted memory
>>> |
>>> PT: Page table
>>> Shared PT: visible to KVM, and the CPU uses it for shared mappings.
>>> Private PT: the CPU uses it, but it is invisible to KVM. TDX module
>>> updates this table to map private guest pages.
>>> Mirrored PT: It is visible to KVM, but the CPU doesn't use it. KVM uses it
>>> to propagate PT change to the actual private PT.
>>>
>>