Re: [PATCH v2] efi, x86: Pass a proper identity mapping in efi_call_phys_prelog
From: Matt Fleming <hidden>
Date: 2013-01-16 14:31:17
Also in:
linux-efi, lkml
(Sorry for the delay in replying to this) On Tue, 2013-01-08 at 09:02 -0600, Nathan Zimmer wrote:
Update efi_call_phys_prelog to install an identity mapping of all available memory. This corrects a bug on very large systems with more then 512 GB in which bios would not be able to access addresses above not in the mapping. The result is a crash that looks much like this. BUG: unable to handle kernel paging request at 000000effd870020 IP: [<0000000078bce331>] 0x78bce330 PGD 0 Oops: 0000 [#1] SMP Modules linked in: CPU 0 Pid: 0, comm: swapper/0 Tainted: G W 3.8.0-rc1-next-20121224-medusa_ntz+ #2 Intel Corp. Stoutland Platform RIP: 0010:[<0000000078bce331>] [<0000000078bce331>] 0x78bce330 RSP: 0000:ffffffff81601d28 EFLAGS: 00010006 RAX: 0000000078b80e18 RBX: 0000000000000004 RCX: 0000000000000004 RDX: 0000000078bcf958 RSI: 0000000000002400 RDI: 8000000000000000 RBP: 0000000078bcf760 R08: 000000effd870000 R09: 0000000000000000 R10: 0000000000000000 R11: 00000000000000c3 R12: 0000000000000030 R13: 000000effd870000 R14: 0000000000000000 R15: ffff88effd870000 FS: 0000000000000000(0000) GS:ffff88effe400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000effd870020 CR3: 000000000160c000 CR4: 00000000000006b0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process swapper/0 (pid: 0, threadinfo ffffffff81600000, task ffffffff81614400) Stack: 0000000078b80d18 0000000000000004 0000000078bced7b ffff880078b81fff 0000000000000000 0000000000000082 0000000078bce3a8 0000000000002400 0000000060000202 0000000078b80da0 0000000078bce45d ffffffff8107cb5a Call Trace: [<ffffffff8107cb5a>] ? on_each_cpu+0x77/0x83 [<ffffffff8102f4eb>] ? change_page_attr_set_clr+0x32f/0x3ed [<ffffffff81035946>] ? efi_call4+0x46/0x80 [<ffffffff816c5abb>] ? efi_enter_virtual_mode+0x1f5/0x305 [<ffffffff816aeb24>] ? start_kernel+0x34a/0x3d2 [<ffffffff816ae5ed>] ? repair_env_string+0x60/0x60 [<ffffffff816ae2be>] ? x86_64_start_reservations+0xba/0xc1 [<ffffffff816ae120>] ? early_idt_handlers+0x120/0x120 [<ffffffff816ae419>] ? x86_64_start_kernel+0x154/0x163 Code: Bad RIP value. RIP [<0000000078bce331>] 0x78bce330 RSP <ffffffff81601d28> CR2: 000000effd870020 ---[ end trace ead828934fef5eab ]--- v2: I noticed a typo on the one sent friday, also ccing the stable tree. Cc: stable@vger.kernel.org Cc: Matt Fleming <redacted> Cc: Thomas Gleixner <redacted> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Signed-off-by: Nathan Zimmer <redacted> Signed-off-by: Robin Holt <redacted> --- arch/x86/platform/efi/efi_64.c | 22 +++++++++++++++++----- 1 files changed, 17 insertions(+), 5 deletions(-)
The last time that the topic of introducing a proper identity pagetable came up was here, https://lkml.org/lkml/2012/10/5/253 mainly in the context of some firmware requiring physical mappings for I/O devices to persist even after we've called SetVirtualAddressMap(). It turns out that there's a bunch of places in the kernel that want this identity mapping - the one you've pointed out being yet another.
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c index 95fd505..2b20038 100644 --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c@@ -38,7 +38,7 @@ #include <asm/cacheflush.h> #include <asm/fixmap.h> -static pgd_t save_pgd __initdata; +static pgd_t *save_pgd __initdata; static unsigned long efi_flags __initdata; static void __init early_code_mapping_set_exec(int executable)@@ -61,12 +61,20 @@ static void __init early_code_mapping_set_exec(int executable) void __init efi_call_phys_prelog(void) { unsigned long vaddress; + int pgd; + int n_pgds; early_code_mapping_set_exec(1); local_irq_save(efi_flags); - vaddress = (unsigned long)__va(0x0UL); - save_pgd = *pgd_offset_k(0x0UL); - set_pgd(pgd_offset_k(0x0UL), *pgd_offset_k(vaddress)); + + n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE); + save_pgd = kmalloc(n_pgds * sizeof(pgd_t), GFP_KERNEL);
There's potential for this to be called under a spinlock, e.g. from phys_efi_get_time(). Maybe this should be GFP_ATOMIC?
quoted hunk ↗ jump to hunk
+ for (pgd = 0; pgd < n_pgds; pgd++) { + save_pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE); + vaddress = (unsigned long)__va(pgd * PGDIR_SIZE); + set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress)); + } __flush_tlb_all(); }@@ -75,7 +83,11 @@ void __init efi_call_phys_epilog(void) /* * After the lock is released, the original page table is restored. */ - set_pgd(pgd_offset_k(0x0UL), save_pgd); + int pgd; + int n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT) , PGDIR_SIZE); + for (pgd = 0; pgd < n_pgds; pgd++) + set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), save_pgd[pgd]); + kfree(save_pgd); __flush_tlb_all(); local_irq_restore(efi_flags); early_code_mapping_set_exec(0);
I initially wrote a patch that was a little like this but Peter suggested making use of trampoline_pgd on x86-64 and switching between pagetables with CR3. While that's certainly the approach we should take going forward, this patch does look pretty trivial (making it suitable for stable) and it fixes a crash. So unless anyone's got an objection I'm happy to queue this up.