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Sun, 7 Jun 2026 04:38:03 +0000 Message-ID: Date: Sat, 6 Jun 2026 21:38:00 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/15] x86/virt/tdx: Add extra memory to TDX Module for Extensions To: Xu Yilun , , , , , CC: , , , , , , , References: <20260522034128.3144354-1-yilun.xu@linux.intel.com> <20260522034128.3144354-3-yilun.xu@linux.intel.com> Content-Language: en-US From: Kishen Maloor In-Reply-To: <20260522034128.3144354-3-yilun.xu@linux.intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4P223CA0016.NAMP223.PROD.OUTLOOK.COM (2603:10b6:303:80::21) To DS0PR11MB8050.namprd11.prod.outlook.com (2603:10b6:8:117::5) Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB8050:EE_|CO1PR11MB4978:EE_ X-MS-Office365-Filtering-Correlation-Id: 0970acd3-1f13-4a90-671a-08dec44e8f8a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016|18002099003|22082099003|11063799006|5023799004|6133799003|4143699003|56012099006|3023799007; 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This makes TDX > Module capable of handling complex tasks through "Extension SEAMCALLs". > Adding more memory to TDX Module is the first step to enable Extensions. > > Currently, TDX Module memory use is relatively static. But, the > Extensions need to use memory more dynamically. While 'static' here > means the kernel provides necessary amount of memory to TDX Module for > its basic functionalities, 'dynamic' means extra memory is needed only > if new add-on features are to be enabled. So add a new memory feeding > process backed by a new SEAMCALL TDH.EXT.MEM.ADD. > > The process is mostly the same as adding PAMT. The kernel queries TDX > Module how much memory needed, allocates it, hands it over, and never > gets it back. > > TDH.EXT.MEM.ADD uses a new parameter type HPA_LIST_INFO to provide > control (private) pages to TDX Module. This type represents a list of > pages for TDX Module to access. It needs a 'root page' which contains > the list of HPAs of the pages. It collapses the HPA of the root page > and the number of valid HPAs into a 64 bit raw value for SEAMCALL > parameters. The root page is always a medium, TDX Module never keeps > the root page. > > Introduce a tdx_clflush_hpa_list() helper to flush shared cache before > SEAMCALL, to avoid shared cache writeback damaging these private pages. > > For now, TDX Module Extensions consumes relatively large amount of > memory (~50MB). Use contiguous page allocation to avoid permanently > fragment too much memory. Print the allocation amount on TDX Module > Extensions initialization for visibility. > > Co-developed-by: Zhenzhong Duan > Signed-off-by: Zhenzhong Duan > Signed-off-by: Xu Yilun > --- > arch/x86/virt/vmx/tdx/tdx.h | 1 + > arch/x86/virt/vmx/tdx/tdx.c | 118 ++++++++++++++++++++++++++++++++++++ > 2 files changed, 119 insertions(+) > > diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h > index a5eec8e3cc71..2335f88bbb10 100644 > --- a/arch/x86/virt/vmx/tdx/tdx.h > +++ b/arch/x86/virt/vmx/tdx/tdx.h > @@ -46,6 +46,7 @@ > #define TDH_PHYMEM_PAGE_WBINVD 41 > #define TDH_VP_WR 43 > #define TDH_SYS_CONFIG 45 > +#define TDH_EXT_MEM_ADD 61 > #define TDH_SYS_DISABLE 69 > > /* > diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c > index c0c6281b08a5..622399d8da68 100644 > --- a/arch/x86/virt/vmx/tdx/tdx.c > +++ b/arch/x86/virt/vmx/tdx/tdx.c > @@ -31,6 +31,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1179,6 +1180,123 @@ static __init int init_tdmrs(struct tdmr_info_list *tdmr_list) > return 0; > } > > +static void tdx_clflush_hpa_list(struct page *root, unsigned int nr_pages) > +{ > + u64 *entries = page_to_virt(root); > + int i; > + > + for (i = 0; i < nr_pages; i++) > + clflush_cache_range(__va(entries[i]), PAGE_SIZE); > +} > + > +#define HPA_LIST_INFO_FIRST_ENTRY GENMASK_U64(11, 3) > +#define HPA_LIST_INFO_PFN GENMASK_U64(51, 12) > +#define HPA_LIST_INFO_LAST_ENTRY GENMASK_U64(63, 55) > + > +static u64 to_hpa_list_info(struct page *root, unsigned int nr_pages) > +{ > + return FIELD_PREP(HPA_LIST_INFO_FIRST_ENTRY, 0) | > + FIELD_PREP(HPA_LIST_INFO_PFN, page_to_pfn(root)) | > + FIELD_PREP(HPA_LIST_INFO_LAST_ENTRY, nr_pages - 1); > +} > + > +static int tdx_ext_mem_add(struct page *root, unsigned int nr_pages) > +{ > + struct tdx_module_args args = { > + .rcx = to_hpa_list_info(root, nr_pages), > + }; > + u64 r; > + > + tdx_clflush_hpa_list(root, nr_pages); > + > + do { > + /* > + * TDH_EXT_MEM_ADD is designed to use output parameter RCX to > + * override/update input parameter RCX, so the caller doesn't > + * have to do manual parameter update on retry call. > + */ > + r = seamcall_ret(TDH_EXT_MEM_ADD, &args); > + } while (r == TDX_INTERRUPTED_RESUMABLE); The retry loop compares the full return value against TDX_INTERRUPTED_RESUMABLE. Should it mask with TDX_SEAMCALL_STATUS_MASK first, in case the module sets any lower detail bits? Ditto for TDH.EXT.INIT in patch 3. > + > + if (r != TDX_SUCCESS) > + return -EFAULT; > + > + return 0; > +} > + > +static int tdx_ext_mem_setup(void) > +{ > + unsigned int nr_pages; > + struct page *page; > + u64 *root; > + unsigned int i; > + int ret; > + > + nr_pages = tdx_sysinfo.ext.memory_pool_required_pages; > + /* > + * memory_pool_required_pages == 0 means no need to add pages, > + * skip the memory setup. > + */ > + if (!nr_pages) > + return 0; > + > + root = kzalloc(PAGE_SIZE, GFP_KERNEL); > + if (!root) > + return -ENOMEM; > + > + page = alloc_contig_pages(nr_pages, GFP_KERNEL, numa_mem_id(), > + &node_online_map); The SEAMCALL takes a scatter list (HPA_LIST_INFO), so the module doesn't require contiguity. If the goal is just to avoid scattering pages across many 2MB regions, maybe dense, 2MB-aligned allocations should achieve that without a single pool-wide contiguous block. > + if (!page) { > + ret = -ENOMEM; > + goto out_free_root; > + } > + > + for (i = 0; i < nr_pages;) { > + unsigned int nents = min(nr_pages - i, > + PAGE_SIZE / sizeof(*root)); > + int j; > + > + for (j = 0; j < nents; j++) > + root[j] = page_to_phys(page + i + j); Would it be better to allocate per-batch (i.e. one root page's worth at a time) rather than the whole pool up front? That way an intermediate TDH.EXT.MEM.ADD failure wouldn't leak all nr_pages. Also, a batch is up to 512 pages (= 2MB) and its allocation could be 2MB-aligned, addressing your fragmentation concern. > + > + ret = tdx_ext_mem_add(virt_to_page(root), nents); > + /* > + * No SEAMCALLs to reclaim the added pages. For simple error > + * handling, leak all pages. > + */ > + WARN_ON_ONCE(ret); > + if (ret) > + break; > + > + i += nents; > + } > + > + /* > + * Extensions memory can't be reclaimed once added, print out the > + * amount, stop tracking it and free the root page, no matter success > + * or failure. > + */ > + pr_info("%lu KB allocated for TDX Module Extensions\n", > + nr_pages * PAGE_SIZE / 1024); > + > +out_free_root: > + kfree(root); > + > + return ret; > +} > + > +static int __maybe_unused init_tdx_ext(void) Could this be named init_tdx_extensions() instead to disambiguate from tdx_ext_init() in patch 3? > +{ > + if (!(tdx_sysinfo.features.tdx_features0 & TDX_FEATURES0_EXT)) > + return 0; > + > + /* No feature requires TDX Module Extensions. */ > + if (!tdx_sysinfo.ext.ext_required) > + return 0; > + > + return tdx_ext_mem_setup(); > +} > + > static __init int init_tdx_module(void) > { > int ret;