From: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Dexuan Cui <decui@microsoft.com>,
"ak@linux.intel.com" <ak@linux.intel.com>,
"arnd@arndb.de" <arnd@arndb.de>, "bp@alien8.de" <bp@alien8.de>,
"brijesh.singh@amd.com" <brijesh.singh@amd.com>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
"dave.hansen@intel.com" <dave.hansen@intel.com>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"jane.chu@oracle.com" <jane.chu@oracle.com>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>,
KY Srinivasan <kys@microsoft.com>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"luto@kernel.org" <luto@kernel.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
"seanjc@google.com" <seanjc@google.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"tony.luck@intel.com" <tony.luck@intel.com>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"Michael Kelley (LINUX)" <mikelley@microsoft.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Tianyu Lan <Tianyu.Lan@microsoft.com>,
"rick.p.edgecombe@intel.com" <rick.p.edgecombe@intel.com>
Subject: Re: [PATCH v8 1/2] x86/tdx: Retry TDVMCALL_MAP_GPA() when needed
Date: Tue, 20 Jun 2023 12:44:06 -0700 [thread overview]
Message-ID: <17ea653f-215d-0bd4-e8b0-5188e5a5ffbd@linux.intel.com> (raw)
In-Reply-To: <SA1PR21MB13359EB1A88FC676C2269318BF5CA@SA1PR21MB1335.namprd21.prod.outlook.com>
Hi,
On 6/20/23 12:23 PM, Dexuan Cui wrote:
>> From: Sathyanarayanan Kuppuswamy
>> Sent: Tuesday, June 20, 2023 11:31 AM
>>> ...
>>> -static bool tdx_enc_status_changed(unsigned long vaddr, int numpages,
>> bool enc)
>>> +static bool tdx_map_gpa(phys_addr_t start, phys_addr_t end, bool enc)
>>> {
>>> - phys_addr_t start = __pa(vaddr);
>>> - phys_addr_t end = __pa(vaddr + numpages * PAGE_SIZE);
>>> + const int max_retries_per_page = 3;
>>
>> Add some details about why you chose 3? Maybe you can also use macro for it.
>
> It's a small number recommended by Kirill:
> https://lwn.net/ml/linux-kernel/20221208194800.n27ak4xj6pmyny46@box.shutemov.name/
>
> The spec doesn't define a max retry count. Normally I guess a max retry count
> of 2 should be enough, at least for Hyper-V according to my testing.
>
> Maybe we can add a comment like this:
>
> /* Retrying the hypercall a second time should succeed; use 3 just in case. */
>
> Does this look good to all?
Looks fine to me.
>
>>> + struct tdx_hypercall_args args;
>>> + u64 map_fail_paddr, ret;
>>> + int retry_count = 0;
>>>
>>> if (!enc) {
>>> /* Set the shared (decrypted) bits: */
>>> @@ -718,12 +720,49 @@ static bool tdx_enc_status_changed(unsigned long
>> vaddr, int numpages, bool enc)
>>> end |= cc_mkdec(0);
>>> }
>>>
>>> - /*
>>> - * Notify the VMM about page mapping conversion. More info about ABI
>>> - * can be found in TDX Guest-Host-Communication Interface (GHCI),
>>> - * section "TDG.VP.VMCALL<MapGPA>"
>>> - */
>>> - if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
>>> + while (retry_count < max_retries_per_page) {
>>> + memset(&args, 0, sizeof(args));
>>> + args.r10 = TDX_HYPERCALL_STANDARD;
>>> + args.r11 = TDVMCALL_MAP_GPA;
>>> + args.r12 = start;
>>> + args.r13 = end - start;
>>> +
>>> + ret = __tdx_hypercall_ret(&args);
>>> + if (ret != TDVMCALL_STATUS_RETRY)
>>> + return !ret;
>>> + /*
>>> + * The guest must retry the operation for the pages in the
>>> + * region starting at the GPA specified in R11. R11 comes
>>> + * from the untrusted VMM. Sanity check it.
>>> + */
>>> + map_fail_paddr = args.r11;
>>
>> Do you really need map_fail_paddr? Why not directly use args.r11?
>>
>>> + if (map_fail_paddr < start || map_fail_paddr >= end)
>>> + return false;
>
> Originally, I used r11.
>
> Dave says " 'r11' needs a real, logical name":
> https://lwn.net/ml/linux-kernel/6bb65614-d420-49d3-312f-316dc8ca4cc4@intel.com/
Got it.
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
next prev parent reply other threads:[~2023-06-20 19:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-20 15:48 [PATCH v8 0/2] Support TDX guests on Hyper-V (the x86/tdx part) Dexuan Cui
2023-06-20 15:48 ` [PATCH v8 1/2] x86/tdx: Retry TDVMCALL_MAP_GPA() when needed Dexuan Cui
2023-06-20 18:30 ` Sathyanarayanan Kuppuswamy
2023-06-20 19:23 ` Dexuan Cui
2023-06-20 19:44 ` Sathyanarayanan Kuppuswamy [this message]
2023-06-20 23:34 ` Dave Hansen
2023-06-21 0:28 ` Dexuan Cui
2023-06-20 15:48 ` [PATCH v8 2/2] x86/tdx: Support vmalloc() for tdx_enc_status_changed() Dexuan Cui
2023-06-20 18:34 ` Sathyanarayanan Kuppuswamy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=17ea653f-215d-0bd4-e8b0-5188e5a5ffbd@linux.intel.com \
--to=sathyanarayanan.kuppuswamy@linux.intel.com \
--cc=Tianyu.Lan@microsoft.com \
--cc=ak@linux.intel.com \
--cc=arnd@arndb.de \
--cc=bp@alien8.de \
--cc=brijesh.singh@amd.com \
--cc=dan.j.williams@intel.com \
--cc=dave.hansen@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=decui@microsoft.com \
--cc=haiyangz@microsoft.com \
--cc=hpa@zytor.com \
--cc=jane.chu@oracle.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=kys@microsoft.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mikelley@microsoft.com \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rick.p.edgecombe@intel.com \
--cc=rostedt@goodmis.org \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=tony.luck@intel.com \
--cc=wei.liu@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).