From 1c8ebc3cbc4f415c5942b32736ecb58ef9c2cc14 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Fri, 3 Jan 2014 16:12:20 -0500 Subject: [BUGFIX][PATCH v3] dbg_rw_guest_mem: need to call put_gfn in error path. Using a 1G hvm domU (in grub) and gdbsx: (gdb) set arch i8086 warning: A handler for the OS ABI "GNU/Linux" is not built into this configuration of GDB. Attempting to continue with the default i8086 settings. The target architecture is assumed to be i8086 (gdb) target remote localhost:9999 Remote debugging using localhost:9999 Remote debugging from host 127.0.0.1 0x0000d475 in ?? () (gdb) x/1xh 0x6ae9168b Will reproduce this bug. With a debug=y build you will get: Assertion '!preempt_count()' failed at preempt.c:37 For a debug=n build you will get a dom0 VCPU hung (at some point) in: [ffff82c4c0126eec] _write_lock+0x3c/0x50 ffff82c4c01e43a0 __get_gfn_type_access+0x150/0x230 ffff82c4c0158885 dbg_rw_mem+0x115/0x360 ffff82c4c0158fc8 arch_do_domctl+0x4b8/0x22f0 ffff82c4c01709ed get_page+0x2d/0x100 ffff82c4c01031aa do_domctl+0x2ba/0x11e0 ffff82c4c0179662 do_mmuext_op+0x8d2/0x1b20 ffff82c4c0183598 __update_vcpu_system_time+0x288/0x340 ffff82c4c015c719 continue_nonidle_domain+0x9/0x30 ffff82c4c012938b add_entry+0x4b/0xb0 ffff82c4c02223f9 syscall_enter+0xa9/0xae And gdb output: (gdb) x/1xh 0x6ae9168b 0x6ae9168b: 0x3024 (gdb) x/1xh 0x6ae9168b 0x6ae9168b: Ignoring packet error, continuing... Reply contains invalid hex digit 116 The 1st one worked because the p2m.lock is recursive and the PCPU had not yet changed. crash reports (for example): crash> mm_rwlock_t 0xffff83083f913010 struct mm_rwlock_t { lock = { raw = { lock = 2147483647 }, debug = {} }, unlock_level = 0, recurse_count = 1, locker = 1, locker_function = 0xffff82c4c022c640 <__func__.13514> "__get_gfn_type_access" } Signed-off-by: Andrew Cooper Signed-off-by: Don Slutz Tested-by: Don Slutz --- Changes v2 to v3: Jan Beulich: Fix flow change (added an else to DBGP2). Ian Campbell: Fix author xen/arch/x86/debug.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/debug.c b/xen/arch/x86/debug.c index a67a192..435bd40 100644 --- a/xen/arch/x86/debug.c +++ b/xen/arch/x86/debug.c @@ -63,10 +63,17 @@ dbg_hvm_va2mfn(dbgva_t vaddr, struct domain *dp, int toaddr, if ( p2m_is_readonly(gfntype) && toaddr ) { DBGP2("kdb:p2m_is_readonly: gfntype:%x\n", gfntype); - return INVALID_MFN; + mfn = INVALID_MFN; + } + else + DBGP2("X: vaddr:%lx domid:%d mfn:%lx\n", vaddr, dp->domain_id, mfn); + + if ( mfn == INVALID_MFN ) + { + put_gfn(dp, *gfn); + *gfn = INVALID_GFN; } - DBGP2("X: vaddr:%lx domid:%d mfn:%lx\n", vaddr, dp->domain_id, mfn); return mfn; } -- 1.8.4