Re: [PATCH v6 08/11] x86/tdx: Add APIs to support Dynamic PAMT ops from KVM's fault path
From: Yan Zhao <hidden>
Date: 2026-07-10 02:47:49
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kvm, linux-doc, lkml
On Fri, Jul 10, 2026 at 09:34:48AM +0800, Edgecombe, Rick P wrote:
On Thu, 2026-07-09 at 15:17 +0800, Yan Zhao wrote:quoted
On Mon, May 25, 2026 at 07:35:12PM -0700, Rick Edgecombe wrote:quoted
When handling an EPT violation, KVM holds a spinlock while manipulating the EPT. Before entering the spinlock it doesn't know how many EPT page tables will need to be installed or whether a huge page will be used. For this reason it allocates a worst case number of page tables that it might need as part of servicing the EPT violation. Under Dynamic PAMT these pre-allocated pages will potentially need to have Dynamic PAMT backing pages installed for them. KVM already has helpers to manage topping up page caches before taking the MMU lock, but they cannot be passed from KVM to arch/x86 code. The problem of how and when to install the DPAMT backing pages for the pages given to the TDX module during the fault path has had a lot of design attempts. - Extracting KVM's MMU caches requires too much inlined code added to headers. - A few varieties of installing Dynamic PAMT backing when allocating the S-EPT page tables. [0][1]IIUC, [0][1] here refer to design attempts that had various problems, right? However, [1] looks exactly like the one being adopted in v6? Did you paste a wrong link? Should [1] instead be https://lore.kernel.org/kvm/20260129011517.3545883-21-seanjc@google.com (local) or https://lore.kernel.org/kvm/aYYCOiMvWfSJR1AL@google.com (local) ?Oh yea... I think it should be: Kai's original idea: https://lore.kernel.org/kvm/aXENNKjAKTM9UJNH@google.com/ (local) Sean's fixup of it: https://lore.kernel.org/kvm/20260129011517.3545883-20-seanjc@google.com/ (local) The problem with Sean's: https://lore.kernel.org/kvm/aYW5CbUvZrLogsWF@yzhao56-desk.sh.intel.com/ (local) TBH I'm a little on the fence about how useful the links will be in general. If someone tries to rip it out, it would be good breadcrumbs I guess
No problem. I am fine with either keeping or removing those links :)