linux-kernel - RE: [PATCH v9 1/2] x86/tdx: Retry TDVMCALL_MAP

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Date:   Thu, 27 Jul 2023 00:19:18 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de" <bp@...en8.de>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>
Subject: RE: [PATCH v9 1/2] x86/tdx: Retry TDVMCALL_MAP_GPA() when needed

> From: Xiaoyao Li <xiaoyao.li@...el.com>
> Sent: Tuesday, July 18, 2023 7:31 PM
> ...
> On 6/22/2023 3:13 AM, Dexuan Cui wrote:
> > GHCI spec for TDX 1.0 says that the MapGPA call may fail with the R10
> > error code = TDG.VP.VMCALL_RETRY (1), and the guest must retry this
> > operation for the pages in the region starting at the GPA specified
> > in R11.
> >
> > When a fully enlightened TDX guest runs on Hyper-V, Hyper-V can return
> > the retry error when set_memory_decrypted() is called to decrypt up to
> > 1GB of swiotlb bounce buffers.
> 
> just out of curiosity, what size does Hyper-v handle at most in one call?

In my test, Hyper-V can process 1 to 9 pages in one call. Most of the time,
Hyper-V only processes 2 pages or 1 page, in one call.

Thanks,
Dexuan