UEFI Specification version 2.9 introduces the concept of memory
acceptance: some Virtual Machine platforms, such as Intel TDX or AMD
SEV-SNP, requiring memory to be accepted before it can be used by the
guest. Accepting happens via a protocol specific for the Virtual
Machine platform.
Accepting memory is costly and it makes VMM allocate memory for the
accepted guest physical address range. It's better to postpone memory
acceptance until memory is needed. It lowers boot time and reduces
memory overhead.
The kernel needs to know what memory has been accepted. Firmware
communicates this information via memory map: a new memory type --
EFI_UNACCEPTED_MEMORY -- indicates such memory.
Range-based tracking works fine for firmware, but it gets bulky for
the kernel: e820 has to be modified on every page acceptance. It leads
to table fragmentation, but there's a limited number of entries in the
e820 table
Another option is to mark such memory as usable in e820 and track if the
range has been accepted in a bitmap. One bit in the bitmap represents
2MiB in the address space: one 4k page is enough to track 64GiB or
physical address space.
In the worst-case scenario -- a huge hole in the middle of the
address space -- It needs 256MiB to handle 4PiB of the address
space.
Any unaccepted memory that is not aligned to 2M gets accepted upfront.
The approach lowers boot time substantially. Boot to shell is ~2.5x
faster for 4G TDX VM and ~4x faster for 64G.
TDX-specific code isolated from the core of unaccepted memory support. It
supposed to help to plug-in different implementation of unaccepted memory
such as SEV-SNP.
The tree can be found here:
https://github.com/intel/tdx.git guest-unaccepted-memory
v6:
- Fix load_unaligned_zeropad() on machine with unaccepted memory;
- Clear PageUnaccepted() on merged pages, leaving it only on head;
- Clarify error handling in allocate_e820();
- Fix build with CONFIG_UNACCEPTED_MEMORY=y, but without TDX;
- Disable kexec at boottime instead of build conflict;
- Rebased to tip/master;
- Spelling fixes;
- Add Reviewed-by from Mike and David;
v5:
- Updates comments and commit messages;
+ Explain options for unaccepted memory handling;
- Expose amount of unaccepted memory in /proc/meminfo
- Adjust check in page_expected_state();
- Fix error code handling in allocate_e820();
- Centralize __pa()/__va() definitions in the boot stub;
- Avoid includes from the main kernel in the boot stub;
- Use an existing hole in boot_param for unaccepted_memory, instead of adding
to the end of the structure;
- Extract allocate_unaccepted_memory() form allocate_e820();
- Complain if there's unaccepted memory, but kernel does not support it;
- Fix vmstat counter;
- Split up few preparatory patches;
- Random readability adjustments;
v4:
- PageBuddyUnaccepted() -> PageUnaccepted;
- Use separate page_type, not shared with offline;
- Rework interface between core-mm and arch code;
- Adjust commit messages;
- Ack from Mike;
Kirill A. Shutemov (15):
x86/boot: Centralize __pa()/__va() definitions
mm: Add support for unaccepted memory
efi/x86: Get full memory map in allocate_e820()
x86/boot: Add infrastructure required for unaccepted memory support
efi/x86: Implement support for unaccepted memory
x86/boot/compressed: Handle unaccepted memory
x86/mm: Reserve unaccepted memory bitmap
x86/mm: Provide helpers for unaccepted memory
x86/mm: Avoid load_unaligned_zeropad() stepping into unaccepted memory
x86/mm: Report unaccepted memory in /proc/meminfo
x86: Disable kexec if system has unaccepted memory
x86/tdx: Make _tdx_hypercall() and __tdx_module_call() available in
boot stub
x86/tdx: Refactor try_accept_one()
x86/tdx: Add unaccepted memory support
mm/vmstat: Add counter for memory accepting
Documentation/x86/zero-page.rst | 1 +
arch/x86/Kconfig | 1 +
arch/x86/boot/bitops.h | 40 +++++++
arch/x86/boot/compressed/Makefile | 1 +
arch/x86/boot/compressed/align.h | 14 +++
arch/x86/boot/compressed/bitmap.c | 43 +++++++
arch/x86/boot/compressed/bitmap.h | 49 ++++++++
arch/x86/boot/compressed/bits.h | 36 ++++++
arch/x86/boot/compressed/compiler.h | 9 ++
arch/x86/boot/compressed/efi.h | 1 +
arch/x86/boot/compressed/find.c | 54 +++++++++
arch/x86/boot/compressed/find.h | 80 +++++++++++++
arch/x86/boot/compressed/ident_map_64.c | 8 --
arch/x86/boot/compressed/kaslr.c | 35 ++++--
arch/x86/boot/compressed/math.h | 37 ++++++
arch/x86/boot/compressed/mem.c | 111 +++++++++++++++++
arch/x86/boot/compressed/minmax.h | 61 ++++++++++
arch/x86/boot/compressed/misc.c | 6 +
arch/x86/boot/compressed/misc.h | 15 +++
arch/x86/boot/compressed/pgtable_types.h | 25 ++++
arch/x86/boot/compressed/sev.c | 2 -
arch/x86/boot/compressed/tdx.c | 78 ++++++++++++
arch/x86/coco/tdx/tdx.c | 94 +++++++--------
arch/x86/include/asm/page.h | 3 +
arch/x86/include/asm/set_memory.h | 2 +
arch/x86/include/asm/shared/tdx.h | 47 ++++++++
arch/x86/include/asm/tdx.h | 19 ---
arch/x86/include/asm/unaccepted_memory.h | 25 ++++
arch/x86/include/uapi/asm/bootparam.h | 2 +-
arch/x86/kernel/e820.c | 10 ++
arch/x86/mm/Makefile | 2 +
arch/x86/mm/init.c | 8 ++
arch/x86/mm/pat/set_memory.c | 2 +-
arch/x86/mm/unaccepted_memory.c | 144 +++++++++++++++++++++++
drivers/firmware/efi/Kconfig | 14 +++
drivers/firmware/efi/efi.c | 1 +
drivers/firmware/efi/libstub/x86-stub.c | 103 +++++++++++++---
include/linux/efi.h | 3 +-
include/linux/page-flags.h | 31 +++++
include/linux/vm_event_item.h | 3 +
mm/internal.h | 12 ++
mm/memblock.c | 9 ++
mm/page_alloc.c | 87 +++++++++++++-
mm/vmstat.c | 3 +
44 files changed, 1215 insertions(+), 116 deletions(-)
create mode 100644 arch/x86/boot/compressed/align.h
create mode 100644 arch/x86/boot/compressed/bitmap.c
create mode 100644 arch/x86/boot/compressed/bitmap.h
create mode 100644 arch/x86/boot/compressed/bits.h
create mode 100644 arch/x86/boot/compressed/compiler.h
create mode 100644 arch/x86/boot/compressed/find.c
create mode 100644 arch/x86/boot/compressed/find.h
create mode 100644 arch/x86/boot/compressed/math.h
create mode 100644 arch/x86/boot/compressed/mem.c
create mode 100644 arch/x86/boot/compressed/minmax.h
create mode 100644 arch/x86/boot/compressed/pgtable_types.h
create mode 100644 arch/x86/include/asm/unaccepted_memory.h
create mode 100644 arch/x86/mm/unaccepted_memory.c
--
2.35.1
Track amount of unaccepted memory and report it in /proc/meminfo.
Signed-off-by: Kirill A. Shutemov <[email protected]>
---
arch/x86/include/asm/set_memory.h | 2 ++
arch/x86/include/asm/unaccepted_memory.h | 9 ++++++
arch/x86/mm/init.c | 8 ++++++
arch/x86/mm/pat/set_memory.c | 2 +-
arch/x86/mm/unaccepted_memory.c | 36 +++++++++++++++++++++++-
5 files changed, 55 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
index 78ca53512486..e467f3941d22 100644
--- a/arch/x86/include/asm/set_memory.h
+++ b/arch/x86/include/asm/set_memory.h
@@ -86,6 +86,8 @@ bool kernel_page_present(struct page *page);
extern int kernel_set_to_readonly;
+void direct_map_meminfo(struct seq_file *m);
+
#ifdef CONFIG_X86_64
/*
* Prevent speculative access to the page by either unmapping
diff --git a/arch/x86/include/asm/unaccepted_memory.h b/arch/x86/include/asm/unaccepted_memory.h
index 89fc91c61560..d8622d952212 100644
--- a/arch/x86/include/asm/unaccepted_memory.h
+++ b/arch/x86/include/asm/unaccepted_memory.h
@@ -3,7 +3,10 @@
#ifndef _ASM_X86_UNACCEPTED_MEMORY_H
#define _ASM_X86_UNACCEPTED_MEMORY_H
+#include <linux/types.h>
+
struct boot_params;
+struct seq_file;
void process_unaccepted_memory(struct boot_params *params, u64 start, u64 num);
@@ -12,5 +15,11 @@ void process_unaccepted_memory(struct boot_params *params, u64 start, u64 num);
void accept_memory(phys_addr_t start, phys_addr_t end);
bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end);
+void unaccepted_meminfo(struct seq_file *m);
+
+#else
+
+static inline void unaccepted_meminfo(struct seq_file *m) {}
+
#endif
#endif
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index d8cfce221275..7e92a9d93994 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -1065,3 +1065,11 @@ unsigned long max_swapfile_size(void)
return pages;
}
#endif
+
+#ifdef CONFIG_PROC_FS
+void arch_report_meminfo(struct seq_file *m)
+{
+ direct_map_meminfo(m);
+ unaccepted_meminfo(m);
+}
+#endif
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 0656db33574d..f08881c4b8ee 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -105,7 +105,7 @@ static void split_page_count(int level)
direct_pages_count[level - 1] += PTRS_PER_PTE;
}
-void arch_report_meminfo(struct seq_file *m)
+void direct_map_meminfo(struct seq_file *m)
{
seq_printf(m, "DirectMap4k: %8lu kB\n",
direct_pages_count[PG_LEVEL_4K] << 2);
diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c
index 33bf70592a46..1ca71eb98c24 100644
--- a/arch/x86/mm/unaccepted_memory.c
+++ b/arch/x86/mm/unaccepted_memory.c
@@ -2,14 +2,17 @@
#include <linux/memblock.h>
#include <linux/mm.h>
#include <linux/pfn.h>
+#include <linux/seq_file.h>
#include <linux/spinlock.h>
+#include <asm/e820/api.h>
#include <asm/io.h>
#include <asm/setup.h>
#include <asm/unaccepted_memory.h>
-/* Protects unaccepted memory bitmap */
+/* Protects unaccepted memory bitmap and nr_unaccepted */
static DEFINE_SPINLOCK(unaccepted_memory_lock);
+static unsigned long nr_unaccepted;
void accept_memory(phys_addr_t start, phys_addr_t end)
{
@@ -63,6 +66,12 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
/* Platform-specific memory-acceptance call goes here */
panic("Cannot accept memory: unknown platform\n");
bitmap_clear(bitmap, range_start, len);
+
+ /* In early boot nr_unaccepted is not yet initialized */
+ if (nr_unaccepted) {
+ WARN_ON(nr_unaccepted < len);
+ nr_unaccepted -= len;
+ }
}
spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
}
@@ -90,3 +99,28 @@ bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end)
return ret;
}
+
+void unaccepted_meminfo(struct seq_file *m)
+{
+ seq_printf(m, "UnacceptedMem: %8lu kB\n",
+ (READ_ONCE(nr_unaccepted) * PMD_SIZE) >> 10);
+}
+
+static int __init unaccepted_init(void)
+{
+ unsigned long *unaccepted_memory;
+ unsigned long flags, bitmap_size;
+
+ if (!boot_params.unaccepted_memory)
+ return 0;
+
+ bitmap_size = e820__end_of_ram_pfn() * PAGE_SIZE / PMD_SIZE;
+ unaccepted_memory = __va(boot_params.unaccepted_memory);
+
+ spin_lock_irqsave(&unaccepted_memory_lock, flags);
+ nr_unaccepted = bitmap_weight(unaccepted_memory, bitmap_size);
+ spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
+
+ return 0;
+}
+fs_initcall(unaccepted_init);
--
2.35.1
On kexec, the target kernel has to know what memory has been accepted.
Information in EFI map is out of date and cannot be used.
boot_params.unaccepted_memory can be used to pass the bitmap between two
kernels on kexec, but the use-case is not yet implemented.
Disable kexec on machines with unaccepted memory for now.
Signed-off-by: Kirill A. Shutemov <[email protected]>
---
arch/x86/mm/unaccepted_memory.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c
index 1ca71eb98c24..b4c43e6089b0 100644
--- a/arch/x86/mm/unaccepted_memory.c
+++ b/arch/x86/mm/unaccepted_memory.c
@@ -1,4 +1,5 @@
// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kexec.h>
#include <linux/memblock.h>
#include <linux/mm.h>
#include <linux/pfn.h>
@@ -114,6 +115,15 @@ static int __init unaccepted_init(void)
if (!boot_params.unaccepted_memory)
return 0;
+#ifdef CONFIG_KEXEC_CORE
+ /*
+ * TODO: Information on memory acceptance status has to be communicated
+ * between kernel.
+ */
+ pr_warn("Disable kexec: not yet supported on systems with unaccepted memory\n");
+ kexec_load_disabled = 1;
+#endif
+
bitmap_size = e820__end_of_ram_pfn() * PAGE_SIZE / PMD_SIZE;
unaccepted_memory = __va(boot_params.unaccepted_memory);
--
2.35.1
On 17.05.22 17:34, Kirill A. Shutemov wrote:
> Track amount of unaccepted memory and report it in /proc/meminfo.
I feel like instead of doing this arch specific tracking here, we should
simply report the total number of unaccepted (base) pages in the buddy.
When the system boots up, the number will rise as unaccepted memory gets
exposed to the buddy. But especially once user space is up and running,
that number should only go down.
Once it hits zero, there is no unaccepted memory left in the buddy and
there won't be any performance surprises anymote -- and AFAIKT, that's
what we really care about.
--
Thanks,
David / dhildenb