linux-kernel - [PATCH] x86/tdx: support VM area addresses for tdx_enc_status

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Message-ID:
 <OS9PR01MB15202A41CF04F0BBF8CE244B48D34A@OS9PR01MB15202.jpnprd01.prod.outlook.com>
Date: Thu, 14 Aug 2025 22:34:02 -0400
From: Shixuan Zhao <shixuan.zhao@...mail.com>
To: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>,
	linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Cc: Shixuan Zhao <shixuan.zhao@...mail.com>
Subject: [PATCH] x86/tdx: support VM area addresses for tdx_enc_status_changed

Currently tdx_enc_status_changed uses __pa which will only accept
addresses within the linear mapping. This patch allows memory allocated
in the VM area to be used.

For VM area addresses, we do it page-by-page since there's no guarantee
that the physical pages are contiguous. If, however, the entire range
falls within the linear mapping, we provide a fast path that do the
entire range just like the current version so that the performance
would remain roughly the same as current.

Signed-off-by: Shixuan Zhao <shixuan.zhao@...mail.com>
---
Hi,

I recently ran into a problem where tdx_enc_status_changed was not
implemented to handle memory mapped in the kernel VM area (e.g., ioremap
or vmalloc). I have created a patch that tries to fix this problem. The
overall idea is to keep a fast path for the current __pa-based routine
if the range falls within the linear mapping, otherwise fall to a page-by-
page page table walk for those in the VM area.

It's the first time I'm submitting a patch to the kernel so although I've
done the RTFM, feel free to discuss or point out anything improper.

Thanks,
Shixuan

 arch/x86/coco/tdx/tdx.c | 42 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 7b2833705..c56cd429f 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -957,15 +957,11 @@ static bool tdx_map_gpa(phys_addr_t start, phys_addr_t end, bool enc)
 }
 
 /*
- * Inform the VMM of the guest's intent for this physical page: shared with
- * the VMM or private to the guest.  The VMM is expected to change its mapping
- * of the page in response.
+ * Helper that works on a paddr range for tdx_enc_status_changed
  */
-static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
+static bool tdx_enc_status_changed_phys(phys_addr_t start, phys_addr_t end,
+					bool enc)
 {
-	phys_addr_t start = __pa(vaddr);
-	phys_addr_t end   = __pa(vaddr + numpages * PAGE_SIZE);
-
 	if (!tdx_map_gpa(start, end, enc))
 		return false;
 
@@ -976,6 +972,38 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
 	return true;
 }
 
+/*
+ * Inform the VMM of the guest's intent for this vaddr range: shared with
+ * the VMM or private to the guest.  The VMM is expected to change its mapping
+ * of the page in response.
+ */
+static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
+{
+	unsigned long va_iter;
+	unsigned long end_va = vaddr + numpages * PAGE_SIZE;
+	phys_addr_t start_pa, end_pa;
+
+	/* fast path when the entire range is within linear mapping */
+	if (virt_addr_valid((void *)vaddr) &&
+	    virt_addr_valid((void *)end_va)) {
+		start_pa = __pa(vaddr);
+		end_pa = __pa(end_va);
+
+		return tdx_enc_status_changed_phys(start_pa, end_pa, enc);
+	}
+
+	/* use page table walk for memory in VM area */
+	for (va_iter = vaddr; va_iter < end_va; va_iter += PAGE_SIZE) {
+		start_pa = slow_virt_to_phys((void *)va_iter);
+		end_pa = start_pa + PAGE_SIZE;
+
+		if (!tdx_enc_status_changed_phys(start_pa, end_pa, enc))
+			return false;
+	}
+
+	return true;
+}
+
 static int tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
 					 bool enc)
 {
-- 
2.43.0