kernel/linux.git/arch/x86/virt, branch v6.19.12

x86: Restrict KVM-induced symbol exports to KVM modules where obvious/possible

2025-11-12T23:29:38+00:00

Extend KVM's export macro framework to provide EXPORT_SYMBOL_FOR_KVM(), and use the helper macro to export symbols for KVM throughout x86 if and only if KVM will build one or more modules, and only for those modules. To avoid unnecessary exports when CONFIG_KVM=m but kvm.ko will not be built (because no vendor modules are selected), let arch code #define EXPORT_SYMBOL_FOR_KVM to suppress/override the exports. Note, the set of symbols to restrict to KVM was generated by manual search and audit; any "misses" are due to human error, not some grand plan. Signed-off-by: Sean Christopherson Signed-off-by: Dave Hansen Acked-by: Kai Huang Tested-by: Kai Huang Link: https://patch.msgid.link/20251112173944.1380633-5-seanjc%40google.com

Merge tag 'x86_tdx_for_6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2025-10-04T17:01:30+00:00

Pull x86 TDX updates from Dave Hansen: "The biggest change here is making TDX and kexec play nicely together. Before this, the memory encryption hardware (which doesn't respect cache coherency) could write back old cachelines on top of data in the new kernel, so kexec and TDX were made mutually exclusive. This removes the limitation. There is also some work to tighten up a hardware bug workaround and some MAINTAINERS updates. - Make TDX and kexec work together - Skip TDX bug workaround when the bug is not present - Update maintainers entries" * tag 'x86_tdx_for_6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/virt/tdx: Use precalculated TDVPR page physical address KVM/TDX: Explicitly do WBINVD when no more TDX SEAMCALLs x86/virt/tdx: Update the kexec section in the TDX documentation x86/virt/tdx: Remove the !KEXEC_CORE dependency x86/kexec: Disable kexec/kdump on platforms with TDX partial write erratum x86/virt/tdx: Mark memory cache state incoherent when making SEAMCALL x86/sme: Use percpu boolean to control WBINVD during kexec x86/kexec: Consolidate relocate_kernel() function parameters x86/tdx: Skip clearing reclaimed pages unless X86_BUG_TDX_PW_MCE is present x86/tdx: Tidy reset_pamt functions x86/tdx: Eliminate duplicate code in tdx_clear_page() MAINTAINERS: Add KVM mail list to the TDX entry MAINTAINERS: Add Rick Edgecombe as a TDX reviewer MAINTAINERS: Update the file list in the TDX entry.

x86/sev: Add new dump_rmp parameter to snp_leak_pages() API

2025-09-17T10:04:04+00:00

When leaking certain page types, such as Hypervisor Fixed (HV_FIXED) pages, it does not make sense to dump RMP contents for the 2MB range of the page(s) being leaked. In the case of HV_FIXED pages, this is not an error situation where the surrounding 2MB page RMP entries can provide debug information. Add new __snp_leak_pages() API with dump_rmp bool parameter to support continue adding pages to the snp_leaked_pages_list but not issue dump_rmpentry(). Make snp_leak_pages() a wrapper for the common case which also allows existing users to continue to dump RMP entries. Suggested-by: Thomas Lendacky Suggested-by: Sean Christopherson Signed-off-by: Ashish Kalra Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Tom Lendacky Acked-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/cover.1758057691.git.ashish.kalra@amd.com

x86/virt/tdx: Use precalculated TDVPR page physical address

2025-09-11T18:38:28+00:00

All of the x86 KVM guest types (VMX, SEV and TDX) do some special context tracking when entering guests. This means that the actual guest entry sequence must be noinstr. Part of entering a TDX guest is passing a physical address to the TDX module. Right now, that physical address is stored as a 'struct page' and converted to a physical address at guest entry. That page=>phys conversion can be complicated, can vary greatly based on kernel config, and it is definitely _not_ a noinstr path today. There have been a number of tinkering approaches to try and fix this up, but they all fall down due to some part of the page=>phys conversion infrastructure not being noinstr friendly. Precalculate the page=>phys conversion and store it in the existing 'tdx_vp' structure. Use the new field at every site that needs a tdvpr physical address. Remove the now redundant tdx_tdvpr_pa(). Remove the __flatten remnant from the tinkering. Note that only one user of the new field is actually noinstr. All others can use page_to_phys(). But, they might as well save the effort since there is a pre-calculated value sitting there for them. [ dhansen: rewrite all the text ] Signed-off-by: Kai Huang Signed-off-by: Dave Hansen Reviewed-by: Kiryl Shutsemau Tested-by: Farrah Chen

KVM/TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

2025-09-05T17:40:41+00:00

On TDX platforms, during kexec, the kernel needs to make sure there are no dirty cachelines of TDX private memory before booting to the new kernel to avoid silent memory corruption to the new kernel. To do this, the kernel has a percpu boolean to indicate whether the cache of a CPU may be in incoherent state. During kexec, namely in stop_this_cpu(), the kernel does WBINVD if that percpu boolean is true. TDX turns on that percpu boolean on a CPU when the kernel does SEAMCALL, Thus making sure the cache will be flushed during kexec. However, kexec has a race condition that, while remaining extremely rare, would be more likely in the presence of a relatively long operation such as WBINVD. In particular, the kexec-ing CPU invokes native_stop_other_cpus() to stop all remote CPUs before booting to the new kernel. native_stop_other_cpus() then sends a REBOOT vector IPI to remote CPUs and waits for them to stop; if that times out, it also sends NMIs to the still-alive CPUs and waits again for them to stop. If the race happens, kexec proceeds before all CPUs have processed the NMI and stopped[1], and the system hangs. But after tdx_disable_virtualization_cpu(), no more TDX activity can happen on this cpu. When kexec is enabled, flush the cache explicitly at that point; this moves the WBINVD to an earlier stage than stop_this_cpus(), avoiding a possibly lengthy operation at a time where it could cause this race. [1] https://lore.kernel.org/kvm/b963fcd60abe26c7ec5dc20b42f1a2ebbcc72397.1750934177.git.kai.huang@intel.com/ [Make the new function a stub for !CONFIG_KEXEC_CORE. - Paolo] Signed-off-by: Kai Huang Signed-off-by: Paolo Bonzini Signed-off-by: Dave Hansen Acked-by: Paolo Bonzini Tested-by: Farrah Chen Link: https://lore.kernel.org/all/20250901160930.1785244-8-pbonzini%40redhat.com

x86/virt/tdx: Mark memory cache state incoherent when making SEAMCALL

2025-09-05T17:40:40+00:00

On TDX platforms, dirty cacheline aliases with and without encryption bits can coexist, and the cpu can flush them back to memory in random order. During kexec, the caches must be flushed before jumping to the new kernel otherwise the dirty cachelines could silently corrupt the memory used by the new kernel due to different encryption property. A percpu boolean is used to mark whether the cache of a given CPU may be in an incoherent state, and the kexec performs WBINVD on the CPUs with that boolean turned on. For TDX, only the TDX module or the TDX guests can generate dirty cachelines of TDX private memory, i.e., they are only generated when the kernel does a SEAMCALL. Set that boolean when the kernel does SEAMCALL so that kexec can flush the cache correctly. The kernel provides both the __seamcall*() assembly functions and the seamcall*() wrapper ones which additionally handle running out of entropy error in a loop. Most of the SEAMCALLs are called using the seamcall*(), except TDH.VP.ENTER and TDH.PHYMEM.PAGE.RDMD which are called using __seamcall*() variant directly. To cover the two special cases, add a new __seamcall_dirty_cache() helper which only sets the percpu boolean and calls the __seamcall*(), and change the special cases to use the new helper. To cover all other SEAMCALLs, change seamcall*() to call the new helper. For the SEAMCALLs invoked via seamcall*(), they can be made from both task context and IRQ disabled context. Given SEAMCALL is just a lengthy instruction (e.g., thousands of cycles) from kernel's point of view and preempt_{disable|enable}() is cheap compared to it, just unconditionally disable preemption during setting the boolean and making SEAMCALL. Signed-off-by: Kai Huang Signed-off-by: Paolo Bonzini Signed-off-by: Dave Hansen Reviewed-by: Chao Gao Reviewed-by: Rick Edgecombe Tested-by: Farrah Chen Link: https://lore.kernel.org/all/20250901160930.1785244-4-pbonzini%40redhat.com

x86/tdx: Skip clearing reclaimed pages unless X86_BUG_TDX_PW_MCE is present

2025-08-22T14:45:50+00:00

Avoid clearing reclaimed TDX private pages unless the platform is affected by the X86_BUG_TDX_PW_MCE erratum. This significantly reduces VM shutdown time on unaffected systems. Background KVM currently clears reclaimed TDX private pages using MOVDIR64B, which: - Clears the TD Owner bit (which identifies TDX private memory) and integrity metadata without triggering integrity violations. - Clears poison from cache lines without consuming it, avoiding MCEs on access (refer TDX Module Base spec. 1348549-006US section 6.5. Handling Machine Check Events during Guest TD Operation). The TDX module also uses MOVDIR64B to initialize private pages before use. If cache flushing is needed, it sets TDX_FEATURES.CLFLUSH_BEFORE_ALLOC. However, KVM currently flushes unconditionally, refer commit 94c477a751c7b ("x86/virt/tdx: Add SEAMCALL wrappers to add TD private pages") In contrast, when private pages are reclaimed, the TDX Module handles flushing via the TDH.PHYMEM.CACHE.WB SEAMCALL. Problem Clearing all private pages during VM shutdown is costly. For guests with a large amount of memory it can take minutes. Solution TDX Module Base Architecture spec. documents that private pages reclaimed from a TD should be initialized using MOVDIR64B, in order to avoid integrity violation or TD bit mismatch detection when later being read using a shared HKID, refer April 2025 spec. "Page Initialization" in section "8.6.2. Platforms not Using ACT: Required Cache Flush and Initialization by the Host VMM" That is an overstatement and will be clarified in coming versions of the spec. In fact, as outlined in "Table 16.2: Non-ACT Platforms Checks on Memory" and "Table 16.3: Non-ACT Platforms Checks on Memory Reads in Li Mode" in the same spec, there is no issue accessing such reclaimed pages using a shared key that does not have integrity enabled. Linux always uses KeyID 0 which never has integrity enabled. KeyID 0 is also the TME KeyID which disallows integrity, refer "TME Policy/Encryption Algorithm" bit description in "Intel Architecture Memory Encryption Technologies" spec version 1.6 April 2025. So there is no need to clear pages to avoid integrity violations. There remains a risk of poison consumption. However, in the context of TDX, it is expected that there would be a machine check associated with the original poisoning. On some platforms that results in a panic. However platforms may support "SEAM_NR" Machine Check capability, in which case Linux machine check handler marks the page as poisoned, which prevents it from being allocated anymore, refer commit 7911f145de5fe ("x86/mce: Implement recovery for errors in TDX/SEAM non-root mode") Improvement By skipping the clearing step on unaffected platforms, shutdown time can improve by up to 40%. On platforms with the X86_BUG_TDX_PW_MCE erratum (SPR and EMR), continue clearing because these platforms may trigger poison on partial writes to previously-private pages, even with KeyID 0, refer commit 1e536e1068970 ("x86/cpu: Detect TDX partial write machine check erratum") Signed-off-by: Adrian Hunter Signed-off-by: Dave Hansen Reviewed-by: Kirill A. Shutemov Reviewed-by: Rick Edgecombe Reviewed-by: Xiaoyao Li Reviewed-by: Binbin Wu Acked-by: Kai Huang Acked-by: Vishal Annapurve Link: https://lore.kernel.org/all/20250819155811.136099-4-adrian.hunter%40intel.com

x86/tdx: Tidy reset_pamt functions

2025-08-22T14:45:50+00:00

tdx_quirk_reset_paddr() was renamed to reflect that, in fact, the clearing is necessary only for hardware with a certain quirk. That is dealt with in a subsequent patch. Rename reset_pamt functions to contain "quirk" to reflect the new functionality, and remove the now misleading comment. Signed-off-by: Adrian Hunter Signed-off-by: Dave Hansen Reviewed-by: Rick Edgecombe Reviewed-by: Binbin Wu Acked-by: Kai Huang Acked-by: Vishal Annapurve Link: https://lore.kernel.org/all/20250819155811.136099-3-adrian.hunter%40intel.com

x86/tdx: Eliminate duplicate code in tdx_clear_page()

2025-08-22T14:45:50+00:00

tdx_clear_page() and reset_tdx_pages() duplicate the TDX page clearing logic. Rename reset_tdx_pages() to tdx_quirk_reset_paddr() and create tdx_quirk_reset_page() to call tdx_quirk_reset_paddr() and be used in place of tdx_clear_page(). The new name reflects that, in fact, the clearing is necessary only for hardware with a certain quirk. That is dealt with in a subsequent patch but doing the rename here avoids additional churn. Note reset_tdx_pages() is slightly different from tdx_clear_page() because, more appropriately, it uses mb() in place of __mb(). Except when extra debugging is enabled (kcsan at present), mb() just calls __mb(). Signed-off-by: Adrian Hunter Signed-off-by: Dave Hansen Reviewed-by: Kirill A. Shutemov Reviewed-by: Binbin Wu Reviewed-by: Xiaoyao Li Reviewed-by: Rick Edgecombe Acked-by: Kai Huang Acked-by: Sean Christopherson Acked-by: Vishal Annapurve Link: https://lore.kernel.org/all/20250819155811.136099-2-adrian.hunter%40intel.com

x86/virt/tdx: Avoid indirect calls to TDX assembly functions

2025-06-10T19:32:52+00:00

Two 'static inline' TDX helper functions (sc_retry() and sc_retry_prerr()) take function pointer arguments which refer to assembly functions. Normally, the compiler inlines the TDX helper, realizes that the function pointer targets are completely static -- thus can be resolved at compile time -- and generates direct call instructions. But, other times (like when CONFIG_CC_OPTIMIZE_FOR_SIZE=y), the compiler declines to inline the helpers and will instead generate indirect call instructions. Indirect calls to assembly functions require special annotation (for various Control Flow Integrity mechanisms). But TDX assembly functions lack the special annotations and can only be called directly. Annotate both the helpers as '__always_inline' to prod the compiler into maintaining the direct calls. There is no guarantee here, but Peter has volunteered to report the compiler bug if this assumption ever breaks[1]. Fixes: 1e66a7e27539 ("x86/virt/tdx: Handle SEAMCALL no entropy error in common code") Fixes: df01f5ae07dd ("x86/virt/tdx: Add SEAMCALL error printing for module initialization") Signed-off-by: Kai Huang Signed-off-by: Dave Hansen Cc: stable@vger.kernel.org Link: https://lore.kernel.org/lkml/20250605145914.GW39944@noisy.programming.kicks-ass.net/ [1] Link: https://lore.kernel.org/all/20250606130737.30713-1-kai.huang%40intel.com