diff options
Diffstat (limited to 'drivers/firmware/efi/unaccepted_memory.c')
-rw-r--r-- | drivers/firmware/efi/unaccepted_memory.c | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c new file mode 100644 index 0000000000..79fb687bb9 --- /dev/null +++ b/drivers/firmware/efi/unaccepted_memory.c @@ -0,0 +1,203 @@ +// SPDX-License-Identifier: GPL-2.0-only + +#include <linux/efi.h> +#include <linux/memblock.h> +#include <linux/spinlock.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); + 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; +} |