From 87da7e66a40532b743cd50972fcf85a1f15b14ea Mon Sep 17 00:00:00 2001 From: Xiao Guangrong Date: Wed, 24 Oct 2012 14:07:59 +0800 Subject: KVM: x86: fix vcpu->mmio_fragments overflow After commit b3356bf0dbb349 (KVM: emulator: optimize "rep ins" handling), the pieces of io data can be collected and write them to the guest memory or MMIO together Unfortunately, kvm splits the mmio access into 8 bytes and store them to vcpu->mmio_fragments. If the guest uses "rep ins" to move large data, it will cause vcpu->mmio_fragments overflow The bug can be exposed by isapc (-M isapc): [23154.818733] general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC [ ......] [23154.858083] Call Trace: [23154.859874] [] kvm_get_cr8+0x1d/0x28 [kvm] [23154.861677] [] kvm_arch_vcpu_ioctl_run+0xcda/0xe45 [kvm] [23154.863604] [] ? kvm_arch_vcpu_load+0x17b/0x180 [kvm] Actually, we can use one mmio_fragment to store a large mmio access then split it when we pass the mmio-exit-info to userspace. After that, we only need two entries to store mmio info for the cross-mmio pages access Signed-off-by: Xiao Guangrong Signed-off-by: Marcelo Tosatti diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1eefebe..224a7e7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3779,7 +3779,7 @@ static int write_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, { struct kvm_mmio_fragment *frag = &vcpu->mmio_fragments[0]; - memcpy(vcpu->run->mmio.data, frag->data, frag->len); + memcpy(vcpu->run->mmio.data, frag->data, min(8u, frag->len)); return X86EMUL_CONTINUE; } @@ -3832,18 +3832,11 @@ mmio: bytes -= handled; val += handled; - while (bytes) { - unsigned now = min(bytes, 8U); - - frag = &vcpu->mmio_fragments[vcpu->mmio_nr_fragments++]; - frag->gpa = gpa; - frag->data = val; - frag->len = now; - - gpa += now; - val += now; - bytes -= now; - } + WARN_ON(vcpu->mmio_nr_fragments >= KVM_MAX_MMIO_FRAGMENTS); + frag = &vcpu->mmio_fragments[vcpu->mmio_nr_fragments++]; + frag->gpa = gpa; + frag->data = val; + frag->len = bytes; return X86EMUL_CONTINUE; } @@ -3890,7 +3883,7 @@ int emulator_read_write(struct x86_emulate_ctxt *ctxt, unsigned long addr, vcpu->mmio_needed = 1; vcpu->mmio_cur_fragment = 0; - vcpu->run->mmio.len = vcpu->mmio_fragments[0].len; + vcpu->run->mmio.len = min(8u, vcpu->mmio_fragments[0].len); vcpu->run->mmio.is_write = vcpu->mmio_is_write = ops->write; vcpu->run->exit_reason = KVM_EXIT_MMIO; vcpu->run->mmio.phys_addr = gpa; @@ -5522,28 +5515,44 @@ static int complete_emulated_pio(struct kvm_vcpu *vcpu) * * read: * for each fragment - * write gpa, len - * exit - * copy data + * for each mmio piece in the fragment + * write gpa, len + * exit + * copy data * execute insn * * write: * for each fragment - * write gpa, len - * copy data - * exit + * for each mmio piece in the fragment + * write gpa, len + * copy data + * exit */ static int complete_emulated_mmio(struct kvm_vcpu *vcpu) { struct kvm_run *run = vcpu->run; struct kvm_mmio_fragment *frag; + unsigned len; BUG_ON(!vcpu->mmio_needed); /* Complete previous fragment */ - frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment++]; + frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment]; + len = min(8u, frag->len); if (!vcpu->mmio_is_write) - memcpy(frag->data, run->mmio.data, frag->len); + memcpy(frag->data, run->mmio.data, len); + + if (frag->len <= 8) { + /* Switch to the next fragment. */ + frag++; + vcpu->mmio_cur_fragment++; + } else { + /* Go forward to the next mmio piece. */ + frag->data += len; + frag->gpa += len; + frag->len -= len; + } + if (vcpu->mmio_cur_fragment == vcpu->mmio_nr_fragments) { vcpu->mmio_needed = 0; if (vcpu->mmio_is_write) @@ -5551,13 +5560,12 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu) vcpu->mmio_read_completed = 1; return complete_emulated_io(vcpu); } - /* Initiate next fragment */ - ++frag; + run->exit_reason = KVM_EXIT_MMIO; run->mmio.phys_addr = frag->gpa; if (vcpu->mmio_is_write) - memcpy(run->mmio.data, frag->data, frag->len); - run->mmio.len = frag->len; + memcpy(run->mmio.data, frag->data, min(8u, frag->len)); + run->mmio.len = min(8u, frag->len); run->mmio.is_write = vcpu->mmio_is_write; vcpu->arch.complete_userspace_io = complete_emulated_mmio; return 0; diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 93bfc9f..ecc5543 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -42,19 +42,8 @@ */ #define KVM_MEMSLOT_INVALID (1UL << 16) -/* - * If we support unaligned MMIO, at most one fragment will be split into two: - */ -#ifdef KVM_UNALIGNED_MMIO -# define KVM_EXTRA_MMIO_FRAGMENTS 1 -#else -# define KVM_EXTRA_MMIO_FRAGMENTS 0 -#endif - -#define KVM_USER_MMIO_SIZE 8 - -#define KVM_MAX_MMIO_FRAGMENTS \ - (KVM_MMIO_SIZE / KVM_USER_MMIO_SIZE + KVM_EXTRA_MMIO_FRAGMENTS) +/* Two fragments for cross MMIO pages. */ +#define KVM_MAX_MMIO_FRAGMENTS 2 /* * For the normal pfn, the highest 12 bits should be zero, -- cgit v0.10.2