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SubjectRe: [PATCH v12 12/22] x86/virt/tdx: Allocate and set up PAMTs for TDMRs
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On 26.06.23 16:12, Kai Huang wrote:
> The TDX module uses additional metadata to record things like which
> guest "owns" a given page of memory. This metadata, referred as
> Physical Address Metadata Table (PAMT), essentially serves as the
> 'struct page' for the TDX module. PAMTs are not reserved by hardware
> up front. They must be allocated by the kernel and then given to the
> TDX module during module initialization.
>
> TDX supports 3 page sizes: 4K, 2M, and 1G. Each "TD Memory Region"
> (TDMR) has 3 PAMTs to track the 3 supported page sizes. Each PAMT must
> be a physically contiguous area from a Convertible Memory Region (CMR).
> However, the PAMTs which track pages in one TDMR do not need to reside
> within that TDMR but can be anywhere in CMRs. If one PAMT overlaps with
> any TDMR, the overlapping part must be reported as a reserved area in
> that particular TDMR.
>
> Use alloc_contig_pages() since PAMT must be a physically contiguous area
> and it may be potentially large (~1/256th of the size of the given TDMR).
> The downside is alloc_contig_pages() may fail at runtime. One (bad)
> mitigation is to launch a TDX guest early during system boot to get
> those PAMTs allocated at early time, but the only way to fix is to add a
> boot option to allocate or reserve PAMTs during kernel boot.
>
> It is imperfect but will be improved on later.
>
> TDX only supports a limited number of reserved areas per TDMR to cover
> both PAMTs and memory holes within the given TDMR. If many PAMTs are
> allocated within a single TDMR, the reserved areas may not be sufficient
> to cover all of them.
>
> Adopt the following policies when allocating PAMTs for a given TDMR:
>
> - Allocate three PAMTs of the TDMR in one contiguous chunk to minimize
> the total number of reserved areas consumed for PAMTs.
> - Try to first allocate PAMT from the local node of the TDMR for better
> NUMA locality.
>
> Also dump out how many pages are allocated for PAMTs when the TDX module
> is initialized successfully. This helps answer the eternal "where did
> all my memory go?" questions.
>
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Reviewed-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
> ---
>
> v11 -> v12:
> - Moved TDX_PS_NUM from tdx.c to <asm/tdx.h> (Kirill)
> - "<= TDX_PS_1G" -> "< TDX_PS_NUM" (Kirill)
> - Changed tdmr_get_pamt() to return base and size instead of base_pfn
> and npages and related code directly (Dave).
> - Simplified PAMT kb counting. (Dave)
> - tdmrs_count_pamt_pages() -> tdmr_count_pamt_kb() (Kirill/Dave)
>
> v10 -> v11:
> - No update
>
> v9 -> v10:
> - Removed code change in disable_tdx_module() as it doesn't exist
> anymore.
>
> v8 -> v9:
> - Added TDX_PS_NR macro instead of open-coding (Dave).
> - Better alignment of 'pamt_entry_size' in tdmr_set_up_pamt() (Dave).
> - Changed to print out PAMTs in "KBs" instead of "pages" (Dave).
> - Added Dave's Reviewed-by.
>
> v7 -> v8: (Dave)
> - Changelog:
> - Added a sentence to state PAMT allocation will be improved.
> - Others suggested by Dave.
> - Moved 'nid' of 'struct tdx_memblock' to this patch.
> - Improved comments around tdmr_get_nid().
> - WARN_ON_ONCE() -> pr_warn() in tdmr_get_nid().
> - Other changes due to 'struct tdmr_info_list'.
>
> v6 -> v7:
> - Changes due to using macros instead of 'enum' for TDX supported page
> sizes.
>
> v5 -> v6:
> - Rebase due to using 'tdx_memblock' instead of memblock.
> - 'int pamt_entry_nr' -> 'unsigned long nr_pamt_entries' (Dave/Sagis).
> - Improved comment around tdmr_get_nid() (Dave).
> - Improved comment in tdmr_set_up_pamt() around breaking the PAMT
> into PAMTs for 4K/2M/1G (Dave).
> - tdmrs_get_pamt_pages() -> tdmrs_count_pamt_pages() (Dave).
>
> - v3 -> v5 (no feedback on v4):
> - Used memblock to get the NUMA node for given TDMR.
> - Removed tdmr_get_pamt_sz() helper but use open-code instead.
> - Changed to use 'switch .. case..' for each TDX supported page size in
> tdmr_get_pamt_sz() (the original __tdmr_get_pamt_sz()).
> - Added printing out memory used for PAMT allocation when TDX module is
> initialized successfully.
> - Explained downside of alloc_contig_pages() in changelog.
> - Addressed other minor comments.
>
>
> ---
> arch/x86/Kconfig | 1 +
> arch/x86/include/asm/tdx.h | 1 +
> arch/x86/virt/vmx/tdx/tdx.c | 215 +++++++++++++++++++++++++++++++++++-
> arch/x86/virt/vmx/tdx/tdx.h | 1 +
> 4 files changed, 213 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 2226d8a4c749..ad364f01de33 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1959,6 +1959,7 @@ config INTEL_TDX_HOST
> depends on KVM_INTEL
> depends on X86_X2APIC
> select ARCH_KEEP_MEMBLOCK
> + depends on CONTIG_ALLOC
> 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/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index d8226a50c58c..91416fd600cd 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -24,6 +24,7 @@
> #define TDX_PS_4K 0
> #define TDX_PS_2M 1
> #define TDX_PS_1G 2
> +#define TDX_PS_NR (TDX_PS_1G + 1)
>
> /*
> * Used to gather the output registers values of the TDCALL and SEAMCALL
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 2ffc1517a93b..fd5417577f26 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -221,7 +221,7 @@ static int tdx_get_sysinfo(struct tdsysinfo_struct *sysinfo,
> * overlap.
> */
> static int add_tdx_memblock(struct list_head *tmb_list, unsigned long start_pfn,
> - unsigned long end_pfn)
> + unsigned long end_pfn, int nid)
> {
> struct tdx_memblock *tmb;
>
> @@ -232,6 +232,7 @@ static int add_tdx_memblock(struct list_head *tmb_list, unsigned long start_pfn,
> INIT_LIST_HEAD(&tmb->list);
> tmb->start_pfn = start_pfn;
> tmb->end_pfn = end_pfn;
> + tmb->nid = nid;
>
> /* @tmb_list is protected by mem_hotplug_lock */
> list_add_tail(&tmb->list, tmb_list);
> @@ -259,9 +260,9 @@ static void free_tdx_memlist(struct list_head *tmb_list)
> static int build_tdx_memlist(struct list_head *tmb_list)
> {
> unsigned long start_pfn, end_pfn;
> - int i, ret;
> + int i, nid, ret;
>
> - for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, NULL) {
> + for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
> /*
> * The first 1MB is not reported as TDX convertible memory.
> * Although the first 1MB is always reserved and won't end up
> @@ -277,7 +278,7 @@ static int build_tdx_memlist(struct list_head *tmb_list)
> * memblock has already guaranteed they are in address
> * ascending order and don't overlap.
> */
> - ret = add_tdx_memblock(tmb_list, start_pfn, end_pfn);
> + ret = add_tdx_memblock(tmb_list, start_pfn, end_pfn, nid);
> if (ret)
> goto err;

Why did you decide to defer remembering the nid as well? I'd just move
that part to the patch that adds add_tdx_memblock().

--
Cheers,

David / dhildenb

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