RE: [PATCH v3 1/3] x86/hyperv: Use slow_virt_to_phys() in page transition hypervisor callback

From: kirill.shutemov@linux.intel.com <redacted> Sent: Monday, January 8, 2024 5:08 AM

On Fri, Jan 05, 2024 at 10:30:23AM -0800, mhkelley58@gmail.com wrote:

quoted

From: Michael Kelley <redacted>

In preparation for temporarily marking pages not present during a
transition between encrypted and decrypted, use slow_virt_to_phys()
in the hypervisor callback. As long as the PFN is correct,
slow_virt_to_phys() works even if the leaf PTE is not present.
The existing functions that depend on vmalloc_to_page() all
require that the leaf PTE be marked present, so they don't work.

Update the comments for slow_virt_to_phys() to note this broader usage
and the requirement to work even if the PTE is not marked present.

Signed-off-by: Michael Kelley <redacted>
---
 arch/x86/hyperv/ivm.c        |  9 ++++++++-
 arch/x86/mm/pat/set_memory.c | 13 +++++++++----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 02e55237d919..8ba18635e338 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c

@@ -524,7 +524,14 @@ static bool hv_vtom_set_host_visibility(unsigned

long kbuffer, int pagecount, bo

quoted

 		return false;

 	for (i = 0, pfn = 0; i < pagecount; i++) {
-		pfn_array[pfn] = virt_to_hvpfn((void *)kbuffer + i * HV_HYP_PAGE_SIZE);
+		/*
+		 * Use slow_virt_to_phys() because the PRESENT bit has been
+		 * temporarily cleared in the PTEs.  slow_virt_to_phys() works
+		 * without the PRESENT bit while virt_to_hvpfn() or similar
+		 * does not.
+		 */
+		pfn_array[pfn] = slow_virt_to_phys((void *)kbuffer +
+					i * HV_HYP_PAGE_SIZE) >> HV_HYP_PAGE_SHIFT;

I think you can make it much more readable by introducing few variables:

		virt = (void *)kbuffer + i * HV_HYPPAGE_SIZE;
		phys = slow_virt_to_phys(virt);
		pfn_array[pfn] = phys >> HV_HYP_PAGE_SHIFT;

Agreed.  I'll do this in the next version.

Michael