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// SPDX-License-Identifier: GPL-2.0-only
#include <linux/efi.h>
#include <linux/memblock.h>
#include <linux/spinlock.h>
#include <linux/crash_dump.h>
#include <linux/nmi.h>
#include <asm/unaccepted_memory.h>
/* Protects unaccepted memory bitmap and accepting_list */
static DEFINE_SPINLOCK(unaccepted_memory_lock);
struct accept_range {
struct list_head list;
unsigned long start;
unsigned long end;
};
static LIST_HEAD(accepting_list);
/*
* accept_memory() -- Consult bitmap and accept the memory if needed.
*
* Only memory that is explicitly marked as unaccepted in the bitmap requires
* an action. All the remaining memory is implicitly accepted and doesn't need
* acceptance.
*
* No need to accept:
* - anything if the system has no unaccepted table;
* - memory that is below phys_base;
* - memory that is above the memory that addressable by the bitmap;
*/
void accept_memory(phys_addr_t start, phys_addr_t end)
{
struct efi_unaccepted_memory *unaccepted;
unsigned long range_start, range_end;
struct accept_range range, *entry;
unsigned long flags;
u64 unit_size;
unaccepted = efi_get_unaccepted_table();
if (!unaccepted)
return;
unit_size = unaccepted->unit_size;
/*
* Only care for the part of the range that is represented
* in the bitmap.
*/
if (start < unaccepted->phys_base)
start = unaccepted->phys_base;
if (end < unaccepted->phys_base)
return;
/* Translate to offsets from the beginning of the bitmap */
start -= unaccepted->phys_base;
end -= unaccepted->phys_base;
/*
* load_unaligned_zeropad() can lead to unwanted loads across page
* boundaries. The unwanted loads are typically harmless. But, they
* might be made to totally unrelated or even unmapped memory.
* load_unaligned_zeropad() relies on exception fixup (#PF, #GP and now
* #VE) to recover from these unwanted loads.
*
* But, this approach does not work for unaccepted memory. For TDX, a
* load from unaccepted memory will not lead to a recoverable exception
* within the guest. The guest will exit to the VMM where the only
* recourse is to terminate the guest.
*
* There are two parts to fix this issue and comprehensively avoid
* access to unaccepted memory. Together these ensure that an extra
* "guard" page is accepted in addition to the memory that needs to be
* used:
*
* 1. Implicitly extend the range_contains_unaccepted_memory(start, end)
* checks up to end+unit_size if 'end' is aligned on a unit_size
* boundary.
*
* 2. Implicitly extend accept_memory(start, end) to end+unit_size if
* 'end' is aligned on a unit_size boundary. (immediately following
* this comment)
*/
if (!(end % unit_size))
end += unit_size;
/* Make sure not to overrun the bitmap */
if (end > unaccepted->size * unit_size * BITS_PER_BYTE)
end = unaccepted->size * unit_size * BITS_PER_BYTE;
range.start = start / unit_size;
range.end = DIV_ROUND_UP(end, unit_size);
retry:
spin_lock_irqsave(&unaccepted_memory_lock, flags);
/*
* Check if anybody works on accepting the same range of the memory.
*
* The check is done with unit_size granularity. It is crucial to catch
* all accept requests to the same unit_size block, even if they don't
* overlap on physical address level.
*/
list_for_each_entry(entry, &accepting_list, list) {
if (entry->end <= range.start)
continue;
if (entry->start >= range.end)
continue;
/*
* Somebody else accepting the range. Or at least part of it.
*
* Drop the lock and retry until it is complete.
*/
spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
goto retry;
}
/*
* Register that the range is about to be accepted.
* Make sure nobody else will accept it.
*/
list_add(&range.list, &accepting_list);
range_start = range.start;
for_each_set_bitrange_from(range_start, range_end, unaccepted->bitmap,
range.end) {
unsigned long phys_start, phys_end;
unsigned long len = range_end - range_start;
phys_start = range_start * unit_size + unaccepted->phys_base;
phys_end = range_end * unit_size + unaccepted->phys_base;
/*
* Keep interrupts disabled until the accept operation is
* complete in order to prevent deadlocks.
*
* Enabling interrupts before calling arch_accept_memory()
* creates an opportunity for an interrupt handler to request
* acceptance for the same memory. The handler will continuously
* spin with interrupts disabled, preventing other task from
* making progress with the acceptance process.
*/
spin_unlock(&unaccepted_memory_lock);
arch_accept_memory(phys_start, phys_end);
spin_lock(&unaccepted_memory_lock);
bitmap_clear(unaccepted->bitmap, range_start, len);
}
list_del(&range.list);
touch_softlockup_watchdog();
spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
}
bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end)
{
struct efi_unaccepted_memory *unaccepted;
unsigned long flags;
bool ret = false;
u64 unit_size;
unaccepted = efi_get_unaccepted_table();
if (!unaccepted)
return false;
unit_size = unaccepted->unit_size;
/*
* Only care for the part of the range that is represented
* in the bitmap.
*/
if (start < unaccepted->phys_base)
start = unaccepted->phys_base;
if (end < unaccepted->phys_base)
return false;
/* Translate to offsets from the beginning of the bitmap */
start -= unaccepted->phys_base;
end -= unaccepted->phys_base;
/*
* Also consider the unaccepted state of the *next* page. See fix #1 in
* the comment on load_unaligned_zeropad() in accept_memory().
*/
if (!(end % unit_size))
end += unit_size;
/* Make sure not to overrun the bitmap */
if (end > unaccepted->size * unit_size * BITS_PER_BYTE)
end = unaccepted->size * unit_size * BITS_PER_BYTE;
spin_lock_irqsave(&unaccepted_memory_lock, flags);
while (start < end) {
if (test_bit(start / unit_size, unaccepted->bitmap)) {
ret = true;
break;
}
start += unit_size;
}
spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
return ret;
}
#ifdef CONFIG_PROC_VMCORE
static bool unaccepted_memory_vmcore_pfn_is_ram(struct vmcore_cb *cb,
unsigned long pfn)
{
return !pfn_is_unaccepted_memory(pfn);
}
static struct vmcore_cb vmcore_cb = {
.pfn_is_ram = unaccepted_memory_vmcore_pfn_is_ram,
};
static int __init unaccepted_memory_init_kdump(void)
{
register_vmcore_cb(&vmcore_cb);
return 0;
}
core_initcall(unaccepted_memory_init_kdump);
#endif /* CONFIG_PROC_VMCORE */
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