linux-kernel - [RFC v3 21/21] x86/boot/compressed/64: use 1GB pages for mappings

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Message-Id: <1682554137-13938-22-git-send-email-anthony.yznaga@oracle.com>
Date:   Wed, 26 Apr 2023 17:08:57 -0700
From:   Anthony Yznaga <anthony.yznaga@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, rppt@...nel.org, akpm@...ux-foundation.org,
        ebiederm@...ssion.com, keescook@...omium.org, graf@...zon.com,
        jason.zeng@...el.com, lei.l.li@...el.com,
        steven.sistare@...cle.com, fam.zheng@...edance.com,
        mgalaxy@...mai.com, kexec@...ts.infradead.org
Subject: [RFC v3 21/21] x86/boot/compressed/64: use 1GB pages for mappings

pkram kaslr code can incur multiple page faults when it walks its
preserved ranges list called via mem_avoid_overlap().  The multiple
faults can easily end up using up the small number of pages available
to be allocated for page table pages.

This patch hacks things so that mappings are 1GB which results in the need
for far fewer page table pages.  As is this breaks AMD SEV-ES which expects
the mappings to be 2M.  This could possibly be fixed by updating split
code to split 1GB page if the aren't any other issues with using 1GB
mappings.

Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
 arch/x86/boot/compressed/ident_map_64.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index 321a5011042d..1e02cf6dda3c 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -95,8 +95,8 @@ void kernel_add_identity_map(unsigned long start, unsigned long end)
 	int ret;
 
 	/* Align boundary to 2M. */
-	start = round_down(start, PMD_SIZE);
-	end = round_up(end, PMD_SIZE);
+	start = round_down(start, PUD_SIZE);
+	end = round_up(end, PUD_SIZE);
 	if (start >= end)
 		return;
 
@@ -120,6 +120,7 @@ void initialize_identity_maps(void *rmode)
 	mapping_info.context = &pgt_data;
 	mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
 	mapping_info.kernpg_flag = _KERNPG_TABLE;
+	mapping_info.direct_gbpages = true;
 
 	/*
 	 * It should be impossible for this not to already be true,
@@ -365,8 +366,8 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
 
 	ghcb_fault = sev_es_check_ghcb_fault(address);
 
-	address   &= PMD_MASK;
-	end        = address + PMD_SIZE;
+	address   &= PUD_MASK;
+	end        = address + PUD_SIZE;
 
 	/*
 	 * Check for unexpected error codes. Unexpected are:
-- 
1.9.4