[PATCH v3 04/24] x86/tdx: Introduce tdx_quirk_reset_folio() to reset private huge pages

[Yan Zhao <yan.y.zhao@intel.com>]

After removing or reclaiming a guest private page or a control page from a
TD, zero the physical page using movdir64b() to enable the kernel to reuse
the pages. This is needed for systems with the X86_BUG_TDX_PW_MCE erratum.

Introduce the function tdx_quirk_reset_folio() to invoke
tdx_quirk_reset_paddr() to convert pages in a huge folio from private back
to normal. The pages start from the page at "start_idx" within a "folio",
spanning "npages" contiguous PFNs.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
RFC v3:
- Rebased to Sean's cleanup series.
- tdx_clear_folio() --> tdx_quirk_reset_folio().

RFC v2:
- Add tdx_clear_folio().
- Drop inner loop _tdx_clear_page() and move __mb() outside of the loop.
  (Rick)
- Use C99-style definition of variables inside a for loop.
- Note: [1] also changes tdx_clear_page(). RFC v2 is not based on [1] now.

[1] https://lore.kernel.org/all/20250724130354.79392-2-adrian.hunter@intel.com

RFC v1:
- split out, let tdx_clear_page() accept level.
---
 arch/x86/include/asm/tdx.h  |  2 ++
 arch/x86/kvm/vmx/tdx.c      |  3 ++-
 arch/x86/virt/vmx/tdx/tdx.c | 11 +++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 7f72fd07f4e5..669dd6d99821 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -147,6 +147,8 @@ static inline bool tdx_supports_demote_nointerrupt(const struct tdx_sys_info *sy
 }
 
 void tdx_quirk_reset_page(struct page *page);
+void tdx_quirk_reset_folio(struct folio *folio, unsigned long start_idx,
+			   unsigned long npages);
 
 int tdx_guest_keyid_alloc(void);
 u32 tdx_get_nr_guest_keyids(void);
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index b369f90dbafa..5b499593edff 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1902,7 +1902,8 @@ static void tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn,
 	if (TDX_BUG_ON(err, TDH_PHYMEM_PAGE_WBINVD, kvm))
 		return;
 
-	tdx_quirk_reset_page(page);
+	tdx_quirk_reset_folio(folio, folio_page_idx(folio, page),
+			      KVM_PAGES_PER_HPAGE(level));
 	tdx_pamt_put(page);
 }
 
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index b57e00c71384..20708f56b1a0 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -800,6 +800,17 @@ static void tdx_quirk_reset_paddr(unsigned long base, unsigned long size)
 	mb();
 }
 
+void tdx_quirk_reset_folio(struct folio *folio, unsigned long start_idx,
+			   unsigned long npages)
+{
+	if (WARN_ON_ONCE(start_idx + npages > folio_nr_pages(folio)))
+		return;
+
+	tdx_quirk_reset_paddr(page_to_phys(folio_page(folio, start_idx)),
+			      npages << PAGE_SHIFT);
+}
+EXPORT_SYMBOL_GPL(tdx_quirk_reset_folio);
+
 void tdx_quirk_reset_page(struct page *page)
 {
 	tdx_quirk_reset_paddr(page_to_phys(page), PAGE_SIZE);
-- 
2.43.2