linux-kernel - Re: [PATCH v13 09/12] mm: x86: Invoke hypercall when page encryption status is changed

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Message-ID: <20210421134924.GB11234@zn.tnic>
Date:   Wed, 21 Apr 2021 15:52:10 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ashish Kalra <ashish.kalra@....com>
Cc:     pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, joro@...tes.org, thomas.lendacky@....com,
        x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        srutherford@...gle.com, seanjc@...gle.com,
        venu.busireddy@...cle.com, brijesh.singh@....com
Subject: Re: [PATCH v13 09/12] mm: x86: Invoke hypercall when page encryption
 status is changed

On Wed, Apr 21, 2021 at 12:12:13PM +0000, Ashish Kalra wrote:
> Yes, both have some common code, but it is only this page level/size
> ...

See below for what I mean. Diff ontop of yours.

> I see that early_set_memory_enc_dec() is also using a for loop, so which
> patches are you referring to ?

The SNP guest set has this pattern:

https://lkml.kernel.org/r/20210408114049.GI10192@zn.tnic

---

diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index b1d59d2b3bf6..e823645101ee 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -232,6 +232,37 @@ void __init sev_setup_arch(void)
 	swiotlb_adjust_size(size);
 }
 
+static unsigned long pg_level_to_pfn(int level, pte_t *kpte, pgprot_t *ret_prot)
+{
+	unsigned long pfn = 0;
+	pgprot_t prot;
+
+	switch (level) {
+	case PG_LEVEL_4K:
+		pfn = pte_pfn(*kpte);
+		prot = pte_pgprot(*kpte);
+		break;
+
+	case PG_LEVEL_2M:
+		pfn = pmd_pfn(*(pmd_t *)kpte);
+		prot = pmd_pgprot(*(pmd_t *)kpte);
+		break;
+
+	case PG_LEVEL_1G:
+		pfn = pud_pfn(*(pud_t *)kpte);
+		prot = pud_pgprot(*(pud_t *)kpte);
+		break;
+
+	default:
+		return 0;
+	}
+
+	if (ret_prot)
+		*ret_prot = prot;
+
+	return pfn;
+}
+
 static void set_memory_enc_dec_hypercall(unsigned long vaddr, int npages,
 					bool enc)
 {
@@ -249,19 +280,9 @@ static void set_memory_enc_dec_hypercall(unsigned long vaddr, int npages,
 		if (!kpte || pte_none(*kpte))
 			return;
 
-		switch (level) {
-		case PG_LEVEL_4K:
-			pfn = pte_pfn(*kpte);
-			break;
-		case PG_LEVEL_2M:
-			pfn = pmd_pfn(*(pmd_t *)kpte);
-			break;
-		case PG_LEVEL_1G:
-			pfn = pud_pfn(*(pud_t *)kpte);
-			break;
-		default:
-			return;
-		}
+		pfn = pg_level_to_pfn(level, kpte, NULL);
+		if (!pfn)
+			continue;
 
 		psize = page_level_size(level);
 		pmask = page_level_mask(level);
@@ -279,22 +300,9 @@ static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
 	unsigned long pfn, pa, size;
 	pte_t new_pte;
 
-	switch (level) {
-	case PG_LEVEL_4K:
-		pfn = pte_pfn(*kpte);
-		old_prot = pte_pgprot(*kpte);
-		break;
-	case PG_LEVEL_2M:
-		pfn = pmd_pfn(*(pmd_t *)kpte);
-		old_prot = pmd_pgprot(*(pmd_t *)kpte);
-		break;
-	case PG_LEVEL_1G:
-		pfn = pud_pfn(*(pud_t *)kpte);
-		old_prot = pud_pgprot(*(pud_t *)kpte);
-		break;
-	default:
+	pfn = pg_level_to_pfn(level, kpte, &old_prot);
+	if (!pfn)
 		return;
-	}
 
 	new_prot = old_prot;
 	if (enc)

-- 
Regards/Gruss,
    Boris.

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