[PATCH 2/2] KVM: TDX: Do not clear poisoned pages

[Adrian Hunter <adrian.hunter@intel.com>]

Skip clearing a private page if it is marked as poisoned.

The machine check architecture may have the capability to recover from
memory corruption in SEAM non-root (i.e. TDX VM guest) mode.  In that
case the page is marked as poisoned, and the TDX Module puts the TDX VM
into a FATAL error state where the only operation permitted is to tear it
down.

During tear down, reclaimed pages are cleared which, in some cases,  helps
to avoid integrity violation or TD bit mismatch detection when later being
read using a shared HKID.

However a poisoned page will never be allocated again, so clearing is not
necessary, and in any case poisoned pages should not be touched.

Note that while it is possible that memory corruption arises from integrity
violation which could be cleared by MOVDIR64B, that is not necessarily the
cause of the machine check.

Suggested-by: Kai Huang <kai.huang@intel.com>
Fixes: 8d032b683c299 ("KVM: TDX: create/destroy VM structure")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 arch/x86/kvm/vmx/tdx.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 457f91b95147..f4263f7a3924 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -282,10 +282,10 @@ static void tdx_clear_page(struct page *page)
 	void *dest = page_to_virt(page);
 	unsigned long i;
 
-	/*
-	 * The page could have been poisoned.  MOVDIR64B also clears
-	 * the poison bit so the kernel can safely use the page again.
-	 */
+	/* Machine check handler may have poisoned the page */
+	if (PageHWPoison(page))
+		return;
+
 	for (i = 0; i < PAGE_SIZE; i += 64)
 		movdir64b(dest + i, zero_page);
 	/*
-- 
2.48.1