linux-kernel - Re: [PATCH v5 11/39] x86/mm: Update pte_modify for _PAGE

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Date:   Fri, 10 Feb 2023 14:57:03 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "bsingharora@...il.com" <bsingharora@...il.com>,
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Subject: Re: [PATCH v5 11/39] x86/mm: Update pte_modify for _PAGE_COW

On Thu, Feb 09, 2023 at 05:09:15PM +0000, Edgecombe, Rick P wrote:
> What do you think, can we leave it or give it a new name? Maybe
> pte_set_dirty() to be more like the x86-only pte_set_flags() family of
> functions?

I'd do this (ontop of yours, not built, not tested, etc). It is short
and sweet:

pte_mkdirty() set both dirty flags
pte_modifl() sets only _PAGE_DIRTY

No special helpers to lookup what they do, no nothing. Plain and simple.

---
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 7942eff2af50..8ba37380966c 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -392,19 +392,10 @@ static inline pte_t pte_mkexec(pte_t pte)
 	return pte_clear_flags(pte, _PAGE_NX);
 }
 
-static inline pte_t __pte_mkdirty(pte_t pte, bool soft)
-{
-	pteval_t dirty = _PAGE_DIRTY;
-
-	if (soft)
-		dirty |= _PAGE_SOFT_DIRTY;
-
-	return pte_set_flags(pte, dirty);
-}
-
+/* Set _PAGE_SOFT_DIRTY for shadow stack pages. */
 static inline pte_t pte_mkdirty(pte_t pte)
 {
-	return __pte_mkdirty(pte, true);
+	return pte_set_flags(pte, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
 }
 
 static inline pte_t pte_mkyoung(pte_t pte)
@@ -749,14 +740,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 
 	pte_result = __pte(val);
 
-	/*
-	 * Dirty bit is not preserved above so it can be done
-	 * in a special way for the shadow stack case, where it
-	 * may need to set _PAGE_COW. __pte_mkdirty() will do this in
-	 * the case of shadow stack.
-	 */
 	if (pte_dirty(pte))
-		pte_result = __pte_mkdirty(pte_result, false);
+		pte_result = pte_set_flags(pte_result, _PAGE_DIRTY);
 
 	return pte_result;
 }



-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette