Re: [PATCH v10 07/16] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory

[Isaku Yamahata]

On Tue, Mar 07, 2023 at 03:13:52AM +1300,
Kai Huang <kai.huang@xxxxxxxxx> wrote:

> As a step of initializing the TDX module, the kernel needs to tell the
> TDX module which memory regions can be used by the TDX module as TDX
> guest memory.
> 
> TDX reports a list of "Convertible Memory Region" (CMR) to tell the
> kernel which memory is TDX compatible.  The kernel needs to build a list
> of memory regions (out of CMRs) as "TDX-usable" memory and pass them to
> the TDX module.  Once this is done, those "TDX-usable" memory regions
> are fixed during module's lifetime.
> 
> To keep things simple, assume that all TDX-protected memory will come
> from the page allocator.  Make sure all pages in the page allocator
> *are* TDX-usable memory.
> 
> As TDX-usable memory is a fixed configuration, take a snapshot of the
> memory configuration from memblocks at the time of module initialization
> (memblocks are modified on memory hotplug).  This snapshot is used to
> enable TDX support for *this* memory configuration only.  Use a memory
> hotplug notifier to ensure that no other RAM can be added outside of
> this configuration.
> 
> This approach requires all memblock memory regions at the time of module
> initialization to be TDX convertible memory to work, otherwise module
> initialization will fail in a later SEAMCALL when passing those regions
> to the module.  This approach works when all boot-time "system RAM" is
> TDX convertible memory, and no non-TDX-convertible memory is hot-added
> to the core-mm before module initialization.
> 
> For instance, on the first generation of TDX machines, both CXL memory
> and NVDIMM are not TDX convertible memory.  Using kmem driver to hot-add
> any CXL memory or NVDIMM to the core-mm before module initialization
> will result in failure to initialize the module.  The SEAMCALL error
> code will be available in the dmesg to help user to understand the
> failure.
> 
> Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> ---
> 
> v9 -> v10:
>  - Moved empty @tdx_memlist check out of is_tdx_memory() to make the
>    logic better.
>  - Added Ying's Reviewed-by.
> 
> v8 -> v9:
>  - Replace "The initial support ..." with timeless sentence in both
>    changelog and comments(Dave).
>  - Fix run-on sentence in changelog, and senstence to explain why to
>    stash off memblock (Dave).
>  - Tried to improve why to choose this approach and how it work in
>    changelog based on Dave's suggestion.
>  - Many other comments enhancement (Dave).
> 
> v7 -> v8:
>  - Trimed down changelog (Dave).
>  - Changed to use PHYS_PFN() and PFN_PHYS() throughout this series
>    (Ying).
>  - Moved memory hotplug handling from add_arch_memory() to
>    memory_notifier (Dan/David).
>  - Removed 'nid' from 'struct tdx_memblock' to later patch (Dave).
>  - {build|free}_tdx_memory() -> {build|}free_tdx_memlist() (Dave).
>  - Removed pfn_covered_by_cmr() check as no code to trim CMRs now.
>  - Improve the comment around first 1MB (Dave).
>  - Added a comment around reserve_real_mode() to point out TDX code
>    relies on first 1MB being reserved (Ying).
>  - Added comment to explain why the new online memory range cannot
>    cross multiple TDX memory blocks (Dave).
>  - Improved other comments (Dave).
> 
> ---
>  arch/x86/Kconfig            |   1 +
>  arch/x86/kernel/setup.c     |   2 +
>  arch/x86/virt/vmx/tdx/tdx.c | 165 +++++++++++++++++++++++++++++++++++-
>  arch/x86/virt/vmx/tdx/tdx.h |   6 ++
>  4 files changed, 172 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 6dd5d5586099..f23bc540778a 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1958,6 +1958,7 @@ config INTEL_TDX_HOST
>  	depends on X86_64
>  	depends on KVM_INTEL
>  	depends on X86_X2APIC
> +	select ARCH_KEEP_MEMBLOCK
>  	help
>  	  Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
>  	  host and certain physical attacks.  This option enables necessary TDX
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 88188549647c..a8a119a9b48c 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1165,6 +1165,8 @@ void __init setup_arch(char **cmdline_p)
>  	 *
>  	 * Moreover, on machines with SandyBridge graphics or in setups that use
>  	 * crashkernel the entire 1M is reserved anyway.
> +	 *
> +	 * Note the host kernel TDX also requires the first 1MB being reserved.
>  	 */
>  	x86_platform.realmode_reserve();
>  
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 981e11492d0e..9149144cd7e7 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -17,6 +17,13 @@
>  #include <linux/spinlock.h>
>  #include <linux/percpu-defs.h>
>  #include <linux/mutex.h>
> +#include <linux/list.h>
> +#include <linux/slab.h>
> +#include <linux/memblock.h>
> +#include <linux/memory.h>
> +#include <linux/minmax.h>
> +#include <linux/sizes.h>
> +#include <linux/pfn.h>
>  #include <asm/msr-index.h>
>  #include <asm/msr.h>
>  #include <asm/page.h>
> @@ -39,6 +46,9 @@ static DEFINE_PER_CPU(unsigned int, tdx_lp_init_status);
>  static enum tdx_module_status_t tdx_module_status;
>  static DEFINE_MUTEX(tdx_module_lock);
>  
> +/* All TDX-usable memory regions.  Protected by mem_hotplug_lock. */
> +static LIST_HEAD(tdx_memlist);
> +
>  /*
>   * Use tdx_global_keyid to indicate that TDX is uninitialized.
>   * This is used in TDX initialization error paths to take it from
> @@ -77,6 +87,54 @@ static int __init record_keyid_partitioning(u32 *tdx_keyid_start,
>  	return 0;
>  }
>  
> +static bool is_tdx_memory(unsigned long start_pfn, unsigned long end_pfn)
> +{
> +	struct tdx_memblock *tmb;
> +
> +	/*
> +	 * This check assumes that the start_pfn<->end_pfn range does not
> +	 * cross multiple @tdx_memlist entries.  A single memory online
> +	 * event across multiple memblocks (from which @tdx_memlist
> +	 * entries are derived at the time of module initialization) is
> +	 * not possible.  This is because memory offline/online is done
> +	 * on granularity of 'struct memory_block', and the hotpluggable
> +	 * memory region (one memblock) must be multiple of memory_block.
> +	 */
> +	list_for_each_entry(tmb, &tdx_memlist, list) {
> +		if (start_pfn >= tmb->start_pfn && end_pfn <= tmb->end_pfn)
> +			return true;
> +	}
> +	return false;
> +}
> +
> +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;
> +
> +	/*
> +	 * Empty list means TDX isn't enabled.  Allow any memory
> +	 * to go online.
> +	 */
> +	if (list_empty(&tdx_memlist))
> +		return NOTIFY_OK;
> +
> +	/*
> +	 * The TDX memory configuration is static and can not be
> +	 * changed.  Reject onlining any memory which is outside of
> +	 * the static configuration whether it supports TDX or not.
> +	 */
> +	return is_tdx_memory(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,
> +};
> +
>  static int __init tdx_init(void)
>  {
>  	u32 tdx_keyid_start, nr_tdx_keyids;
> @@ -107,6 +165,13 @@ static int __init tdx_init(void)
>  		goto no_tdx;
>  	}
>  
> +	err = register_memory_notifier(&tdx_memory_nb);
> +	if (err) {
> +		pr_info("initialization failed: register_memory_notifier() failed (%d)\n",
> +				err);
> +		goto no_tdx;
> +	}
> +
>  	tdx_guest_keyid_start = tdx_keyid_start;
>  	tdx_nr_guest_keyids = nr_tdx_keyids;
>  
> @@ -316,6 +381,79 @@ static int tdx_get_sysinfo(struct tdsysinfo_struct *sysinfo,
>  	return 0;
>  }
>  
> +/*
> + * Add a memory region as a TDX memory block.  The caller must make sure
> + * all memory regions are added in address ascending order and don't
> + * overlap.
> + */
> +static int add_tdx_memblock(struct list_head *tmb_list, unsigned long start_pfn,
> +			    unsigned long end_pfn)
> +{
> +	struct tdx_memblock *tmb;
> +
> +	tmb = kmalloc(sizeof(*tmb), GFP_KERNEL);
> +	if (!tmb)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&tmb->list);
> +	tmb->start_pfn = start_pfn;
> +	tmb->end_pfn = end_pfn;
> +
> +	/* @tmb_list is protected by mem_hotplug_lock */
> +	list_add_tail(&tmb->list, tmb_list);
> +	return 0;
> +}
> +
> +static void free_tdx_memlist(struct list_head *tmb_list)
> +{
> +	/* @tmb_list is protected by mem_hotplug_lock */
> +	while (!list_empty(tmb_list)) {
> +		struct tdx_memblock *tmb = list_first_entry(tmb_list,
> +				struct tdx_memblock, list);
> +
> +		list_del(&tmb->list);
> +		kfree(tmb);
> +	}
> +}
> +
> +/*
> + * Ensure that all memblock memory regions are convertible to TDX
> + * memory.  Once this has been established, stash the memblock
> + * ranges off in a secondary structure because memblock is modified
> + * in memory hotplug while TDX memory regions are fixed.
> + */
> +static int build_tdx_memlist(struct list_head *tmb_list)
> +{
> +	unsigned long start_pfn, end_pfn;
> +	int i, ret;
> +
> +	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, NULL) {
> +		/*
> +		 * The first 1MB is not reported as TDX convertible memory.
> +		 * Although the first 1MB is always reserved and won't end up
> +		 * to the page allocator, it is still in memblock's memory
> +		 * regions.  Skip them manually to exclude them as TDX memory.
> +		 */
> +		start_pfn = max(start_pfn, PHYS_PFN(SZ_1M));
> +		if (start_pfn >= end_pfn)
> +			continue;
> +
> +		/*
> +		 * Add the memory regions as TDX memory.  The regions in
> +		 * memblock has already guaranteed they are in address
> +		 * ascending order and don't overlap.
> +		 */
> +		ret = add_tdx_memblock(tmb_list, start_pfn, end_pfn);
> +		if (ret)
> +			goto err;
> +	}
> +
> +	return 0;
> +err:
> +	free_tdx_memlist(tmb_list);
> +	return ret;
> +}
> +
>  static int init_tdx_module(void)
>  {
>  	static DECLARE_PADDED_STRUCT(tdsysinfo_struct, tdsysinfo,
> @@ -329,10 +467,25 @@ static int init_tdx_module(void)
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * To keep things simple, assume that all TDX-protected memory
> +	 * will come from the page allocator.  Make sure all pages in the
> +	 * page allocator are TDX-usable memory.
> +	 *
> +	 * Build the list of "TDX-usable" memory regions which cover all
> +	 * pages in the page allocator to guarantee that.  Do it while
> +	 * holding mem_hotplug_lock read-lock as the memory hotplug code
> +	 * path reads the @tdx_memlist to reject any new memory.
> +	 */
> +	get_online_mems();
> +
> +	ret = build_tdx_memlist(&tdx_memlist);
> +	if (ret)
> +		goto out;
> +
>  	/*
>  	 * TODO:
>  	 *
> -	 *  - Build the list of TDX-usable memory regions.
>  	 *  - Construct a list of "TD Memory Regions" (TDMRs) to cover
>  	 *    all TDX-usable memory regions.
>  	 *  - Configure the TDMRs and the global KeyID to the TDX module.
> @@ -341,7 +494,15 @@ static int init_tdx_module(void)
>  	 *
>  	 *  Return error before all steps are done.
>  	 */
> -	return -EINVAL;
> +	ret = -EINVAL;
> +out:
> +	/*
> +	 * @tdx_memlist is written here and read at memory hotplug time.
> +	 * Lock out memory hotplug code while building it.
> +	 */
> +	put_online_mems();
> +
> +	return ret;
>  }
>  
>  static int __tdx_enable(void)
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index 2f2d8737a364..6518024fcb68 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -101,6 +101,12 @@ enum tdx_module_status_t {
>  	TDX_MODULE_ERROR
>  };
>  
> +struct tdx_memblock {
> +	struct list_head list;
> +	unsigned long start_pfn;
> +	unsigned long end_pfn;
> +};
> +
>  struct tdx_module_output;
>  u64 __seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
>  	       struct tdx_module_output *out);
> -- 
> 2.39.2
> 

Reviewed-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>