linux-kernel - Re: [PATCH] x86/mm: Rewrite sme_populate

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Date:   Mon, 4 Dec 2017 20:39:31 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Borislav Petkov <bp@...e.de>,
        Brijesh Singh <brijesh.singh@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm: Rewrite sme_populate_pgd() in a more sensible way

On Mon, Dec 04, 2017 at 04:34:45PM +0000, Kirill A. Shutemov wrote:
> On Mon, Dec 04, 2017 at 04:00:26PM +0000, Tom Lendacky wrote:
> > On 12/4/2017 8:57 AM, Kirill A. Shutemov wrote:
> > > On Mon, Dec 04, 2017 at 08:19:11AM -0600, Tom Lendacky wrote:
> > > > On 12/4/2017 5:23 AM, Kirill A. Shutemov wrote:
> > > > > sme_populate_pgd() open-codes a lot of things that are not needed to be
> > > > > open-coded.
> > > > > 
> > > > > Let's rewrite it in a more stream-lined way.
> > > > > 
> > > > > This would also buy us boot-time switching between support between
> > > > > paging modes, when rest of the pieces will be upstream.
> > > > 
> > > > Hi Kirill,
> > > > 
> > > > Unfortunately, some of these can't be changed.  The use of p4d_offset(),
> > > > pud_offset(), etc., use non-identity mapped virtual addresses which cause
> > > > failures at this point of the boot process.
> > > 
> > > Wat? Virtual address is virtual address. p?d_offset() doesn't care about
> > > what mapping you're using.
> > 
> > Yes it does.  For example, pmd_offset() issues a pud_page_addr() call,
> > which does a __va() returning a non-identity mapped address (0xffff88...).
> > Only identity mapped virtual addresses have been setup at this point, so
> > the use of that virtual address panics the kernel.
> 
> Stupid me. You are right.
> 
> What about something like this:

sme_pgtable_calc() also looks unnecessary complex.

Any objections on this:

diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 65e0d68f863f..59b7d7ba9b37 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -548,8 +548,7 @@ static void __init *sme_populate_pgd(pgd_t *pgd_base, void *pgtable_area,
 
 static unsigned long __init sme_pgtable_calc(unsigned long len)
 {
-	unsigned long p4d_size, pud_size, pmd_size;
-	unsigned long total;
+	unsigned long entries, tables;
 
 	/*
 	 * Perform a relatively simplistic calculation of the pagetable
@@ -559,41 +558,25 @@ static unsigned long __init sme_pgtable_calc(unsigned long len)
 	 * mappings. Incrementing the count for each covers the case where
 	 * the addresses cross entries.
 	 */
-	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
-		p4d_size = (ALIGN(len, PGDIR_SIZE) / PGDIR_SIZE) + 1;
-		p4d_size *= sizeof(p4d_t) * PTRS_PER_P4D;
-		pud_size = (ALIGN(len, P4D_SIZE) / P4D_SIZE) + 1;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	} else {
-		p4d_size = 0;
-		pud_size = (ALIGN(len, PGDIR_SIZE) / PGDIR_SIZE) + 1;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	}
-	pmd_size = (ALIGN(len, PUD_SIZE) / PUD_SIZE) + 1;
-	pmd_size *= sizeof(pmd_t) * PTRS_PER_PMD;
 
-	total = p4d_size + pud_size + pmd_size;
+        entries = (DIV_ROUND_UP(len, PGDIR_SIZE) + 1) * PAGE_SIZE;
+        if (PTRS_PER_P4D > 1)
+                entries += (DIV_ROUND_UP(len, P4D_SIZE) + 1) * PAGE_SIZE;
+        entries += (DIV_ROUND_UP(len, PUD_SIZE) + 1) * PAGE_SIZE;
+        entries += (DIV_ROUND_UP(len, PMD_SIZE) + 1) * PAGE_SIZE;
 
 	/*
 	 * Now calculate the added pagetable structures needed to populate
 	 * the new pagetables.
 	 */
-	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
-		p4d_size = ALIGN(total, PGDIR_SIZE) / PGDIR_SIZE;
-		p4d_size *= sizeof(p4d_t) * PTRS_PER_P4D;
-		pud_size = ALIGN(total, P4D_SIZE) / P4D_SIZE;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	} else {
-		p4d_size = 0;
-		pud_size = ALIGN(total, PGDIR_SIZE) / PGDIR_SIZE;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	}
-	pmd_size = ALIGN(total, PUD_SIZE) / PUD_SIZE;
-	pmd_size *= sizeof(pmd_t) * PTRS_PER_PMD;
 
-	total += p4d_size + pud_size + pmd_size;
+        tables = DIV_ROUND_UP(entries, PGDIR_SIZE) * PAGE_SIZE;
+        if (PTRS_PER_P4D > 1)
+                tables += DIV_ROUND_UP(entries, P4D_SIZE) * PAGE_SIZE;
+        tables += DIV_ROUND_UP(entries, PUD_SIZE) * PAGE_SIZE;
+        tables += DIV_ROUND_UP(entries, PMD_SIZE) * PAGE_SIZE;
 
-	return total;
+	return entries + tables;
 }
 
 void __init sme_encrypt_kernel(void)
-- 
 Kirill A. Shutemov