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Message-ID: <8300f1098aa8fbfae711313be41ee44cb1203d62.camel@intel.com> Date: Mon, 28 Nov 2022 09:21:05 +0000 From: "Huang, Kai" <kai.huang@...el.com> To: "Williams, Dan J" <dan.j.williams@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "david@...hat.com" <david@...hat.com> CC: "Hansen, Dave" <dave.hansen@...el.com>, "Luck, Tony" <tony.luck@...el.com>, "bagasdotme@...il.com" <bagasdotme@...il.com>, "ak@...ux.intel.com" <ak@...ux.intel.com>, "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>, "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>, "Christopherson,, Sean" <seanjc@...gle.com>, "Chatre, Reinette" <reinette.chatre@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "Yamahata, Isaku" <isaku.yamahata@...el.com>, "peterz@...radead.org" <peterz@...radead.org>, "imammedo@...hat.com" <imammedo@...hat.com>, "Gao, Chao" <chao.gao@...el.com>, "Brown, Len" <len.brown@...el.com>, "Shahar, Sagi" <sagis@...gle.com>, "sathyanarayanan.kuppuswamy@...ux.intel.com" <sathyanarayanan.kuppuswamy@...ux.intel.com>, "Huang, Ying" <ying.huang@...el.com> Subject: Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory On Mon, 2022-11-28 at 09:43 +0100, David Hildenbrand wrote: > On 28.11.22 09:38, Huang, Kai wrote: > > On Fri, 2022-11-25 at 10:28 +0100, David Hildenbrand wrote: > > > On 24.11.22 10:06, Huang, Kai wrote: > > > > On Wed, 2022-11-23 at 17:50 -0800, Dan Williams wrote: > > > > > > > > > > > > @@ -968,6 +969,15 @@ int arch_add_memory(int nid, u64 start, u64 size, > > > > > > unsigned long start_pfn = start >> PAGE_SHIFT; > > > > > > unsigned long nr_pages = size >> PAGE_SHIFT; > > > > > > > > > > > > + /* > > > > > > + * For now if TDX is enabled, all pages in the page allocator > > > > > > + * must be TDX memory, which is a fixed set of memory regions > > > > > > + * that are passed to the TDX module. Reject the new region > > > > > > + * if it is not TDX memory to guarantee above is true. > > > > > > + */ > > > > > > + if (!tdx_cc_memory_compatible(start_pfn, start_pfn + nr_pages)) > > > > > > + return -EINVAL; > > > > > > > > > > arch_add_memory() does not add memory to the page allocator. For > > > > > example, memremap_pages() uses arch_add_memory() and explicitly does not > > > > > release the memory to the page allocator. > > > > > > > > Indeed. Sorry I missed this. > > > > > > > > > This check belongs in > > > > > add_memory_resource() to prevent new memory that violates TDX from being > > > > > onlined. > > > > > > > > This would require adding another 'arch_cc_memory_compatible()' to the common > > > > add_memory_resource() (I actually long time ago had such patch to work with the > > > > memremap_pages() you mentioned above). > > > > > > > > How about adding a memory_notifier to the TDX code, and reject online of TDX > > > > incompatible memory (something like below)? The benefit is this is TDX code > > > > self contained and won't pollute the common mm code: > > > > > > > > +static int tdx_memory_notifier(struct notifier_block *nb, > > > > + unsigned long action, void *v) > > > > +{ > > > > + struct memory_notify *mn = v; > > > > + > > > > + if (action != MEM_GOING_ONLINE) > > > > + return NOTIFY_OK; > > > > + > > > > + /* > > > > + * Not all memory is compatible with TDX. Reject > > > > + * online of any incompatible memory. > > > > + */ > > > > + return tdx_cc_memory_compatible(mn->start_pfn, > > > > + mn->start_pfn + mn->nr_pages) ? NOTIFY_OK : NOTIFY_BAD; > > > > +} > > > > + > > > > +static struct notifier_block tdx_memory_nb = { > > > > + .notifier_call = tdx_memory_notifier, > > > > +}; > > > > > > With mhp_memmap_on_memory() some memory might already be touched during > > > add_memory() (because part of the hotplug memory is used for holding the > > > memmap), not when actually onlining memory. So in that case, this would > > > be too late. > > > > Hi David, > > > > Thanks for the review! > > > > Right. The memmap pages are added to the zone before online_pages(), but IIUC > > those memmap pages will never be free pages thus won't be allocated by the page > > allocator, correct? Therefore in practice there won't be problem even they are > > not TDX compatible memory. > > But that memory will be read/written. Isn't that an issue, for example, > if memory doesn't get accepted etc? > Sorry I don't quite understand "if memory doesn't get accepted" mean. Do you mean accepted by the TDX module? Only the host kernel will read/write those memmap pages. The TDX module won't (as they won't be allocated to be used as TDX guest memory or TDX module metadata). So it's fine.
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