KVM: PPC: Protect kvm_vcpu_read_guest with srcu locks

The kvm_vcpu_read_guest/kvm_vcpu_write_guest used for nested guests
eventually call srcu_dereference_check to dereference a memslot and
lockdep produces a warning as neither kvm->slots_lock nor
kvm->srcu lock is held and kvm->users_count is above zero (>100 in fact).

This wraps mentioned VCPU read/write helpers in srcu read lock/unlock as
it is done in other places. This uses vcpu->srcu_idx when possible.

These helpers are only used for nested KVM so this may explain why
we did not see these before.

Here is an example of a warning:

=============================
WARNING: suspicious RCU usage
5.7.0-rc3-le_dma-bypass.3.2_a+fstn1 #897 Not tainted
-----------------------------
include/linux/kvm_host.h:633 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by qemu-system-ppc/2752:
 #0: c000200359016be0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x144/0xd80 [kvm]

stack backtrace:
CPU: 80 PID: 2752 Comm: qemu-system-ppc Not tainted 5.7.0-rc3-le_dma-bypass.3.2_a+fstn1 #897
Call Trace:
[c0002003591ab240] [c000000000b23ab4] dump_stack+0x190/0x25c (unreliable)
[c0002003591ab2b0] [c00000000023f954] lockdep_rcu_suspicious+0x140/0x164
[c0002003591ab330] [c008000004a445f8] kvm_vcpu_gfn_to_memslot+0x4c0/0x510 [kvm]
[c0002003591ab3a0] [c008000004a44c18] kvm_vcpu_read_guest+0xa0/0x180 [kvm]
[c0002003591ab410] [c008000004ff9bd8] kvmhv_enter_nested_guest+0x90/0xb80 [kvm_hv]
[c0002003591ab980] [c008000004fe07bc] kvmppc_pseries_do_hcall+0x7b4/0x1c30 [kvm_hv]
[c0002003591aba10] [c008000004fe5d30] kvmppc_vcpu_run_hv+0x10a8/0x1a30 [kvm_hv]
[c0002003591abae0] [c008000004a5d954] kvmppc_vcpu_run+0x4c/0x70 [kvm]
[c0002003591abb10] [c008000004a56e54] kvm_arch_vcpu_ioctl_run+0x56c/0x7c0 [kvm]
[c0002003591abba0] [c008000004a3ddc4] kvm_vcpu_ioctl+0x4ac/0xd80 [kvm]
[c0002003591abd20] [c0000000006ebb58] ksys_ioctl+0x188/0x210
[c0002003591abd70] [c0000000006ebc28] sys_ioctl+0x48/0xb0
[c0002003591abdb0] [c000000000042764] system_call_exception+0x1d4/0x2e0
[c0002003591abe20] [c00000000000cce8] system_call_common+0xe8/0x214

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 3cb0c98..c6b3390 100644 (file)
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -160,7 +160,9 @@ int kvmppc_mmu_walk_radix_tree(struct kvm_vcpu *vcpu, gva_t eaddr,
                        return -EINVAL;
                /* Read the entry from guest memory */
                addr = base + (index * sizeof(rpte));
+               vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
                ret = kvm_read_guest(kvm, addr, &rpte, sizeof(rpte));
+               srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
                if (ret) {
                        if (pte_ret_p)
                                *pte_ret_p = addr;
@@ -236,7 +238,9 @@ int kvmppc_mmu_radix_translate_table(struct kvm_vcpu *vcpu, gva_t eaddr,
 
        /* Read the table to find the root of the radix tree */
        ptbl = (table & PRTB_MASK) + (table_index * sizeof(entry));
+       vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
        ret = kvm_read_guest(kvm, ptbl, &entry, sizeof(entry));
+       srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
        if (ret)
                return ret;
 

diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index 2c849a6..6822d23 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -233,20 +233,21 @@ long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
 
        /* copy parameters in */
        hv_ptr = kvmppc_get_gpr(vcpu, 4);
+       regs_ptr = kvmppc_get_gpr(vcpu, 5);
+       vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
        err = kvm_vcpu_read_guest(vcpu, hv_ptr, &l2_hv,
-                                 sizeof(struct hv_guest_state));
+                                 sizeof(struct hv_guest_state)) ||
+               kvm_vcpu_read_guest(vcpu, regs_ptr, &l2_regs,
+                                   sizeof(struct pt_regs));
+       srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
        if (err)
                return H_PARAMETER;
+
        if (kvmppc_need_byteswap(vcpu))
                byteswap_hv_regs(&l2_hv);
        if (l2_hv.version != HV_GUEST_STATE_VERSION)
                return H_P2;
 
-       regs_ptr = kvmppc_get_gpr(vcpu, 5);
-       err = kvm_vcpu_read_guest(vcpu, regs_ptr, &l2_regs,
-                                 sizeof(struct pt_regs));
-       if (err)
-               return H_PARAMETER;
        if (kvmppc_need_byteswap(vcpu))
                byteswap_pt_regs(&l2_regs);
        if (l2_hv.vcpu_token >= NR_CPUS)
@@ -323,12 +324,12 @@ long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu)
                byteswap_hv_regs(&l2_hv);
                byteswap_pt_regs(&l2_regs);
        }
+       vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
        err = kvm_vcpu_write_guest(vcpu, hv_ptr, &l2_hv,
-                                  sizeof(struct hv_guest_state));
-       if (err)
-               return H_AUTHORITY;
-       err = kvm_vcpu_write_guest(vcpu, regs_ptr, &l2_regs,
+                                  sizeof(struct hv_guest_state)) ||
+               kvm_vcpu_write_guest(vcpu, regs_ptr, &l2_regs,
                                   sizeof(struct pt_regs));
+       srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
        if (err)
                return H_AUTHORITY;
 
@@ -508,12 +509,16 @@ long kvmhv_copy_tofrom_guest_nested(struct kvm_vcpu *vcpu)
                        goto not_found;
 
                /* Write what was loaded into our buffer back to the L1 guest */
+               vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
                rc = kvm_vcpu_write_guest(vcpu, gp_to, buf, n);
+               srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
                if (rc)
                        goto not_found;
        } else {
                /* Load the data to be stored from the L1 guest into our buf */
+               vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
                rc = kvm_vcpu_read_guest(vcpu, gp_from, buf, n);
+               srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
                if (rc)
                        goto not_found;
 
@@ -548,9 +553,12 @@ static void kvmhv_update_ptbl_cache(struct kvm_nested_guest *gp)
 
        ret = -EFAULT;
        ptbl_addr = (kvm->arch.l1_ptcr & PRTB_MASK) + (gp->l1_lpid << 4);
-       if (gp->l1_lpid < (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 8)))
+       if (gp->l1_lpid < (1ul << ((kvm->arch.l1_ptcr & PRTS_MASK) + 8))) {
+               int srcu_idx = srcu_read_lock(&kvm->srcu);
                ret = kvm_read_guest(kvm, ptbl_addr,
                                     &ptbl_entry, sizeof(ptbl_entry));
+               srcu_read_unlock(&kvm->srcu, srcu_idx);
+       }
        if (ret) {
                gp->l1_gr_to_hr = 0;
                gp->process_table = 0;

diff --git a/arch/powerpc/kvm/book3s_rtas.c b/arch/powerpc/kvm/book3s_rtas.c
index 26b2599..c5e6775 100644 (file)
--- a/arch/powerpc/kvm/book3s_rtas.c
+++ b/arch/powerpc/kvm/book3s_rtas.c
@@ -229,7 +229,9 @@ int kvmppc_rtas_hcall(struct kvm_vcpu *vcpu)
         */
        args_phys = kvmppc_get_gpr(vcpu, 4) & KVM_PAM;
 
+       vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
        rc = kvm_read_guest(vcpu->kvm, args_phys, &args, sizeof(args));
+       srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
        if (rc)
                goto fail;
 

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index dd7d141..d7b6978 100644 (file)
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -403,7 +403,10 @@ int kvmppc_ld(struct kvm_vcpu *vcpu, ulong *eaddr, int size, void *ptr,
                return EMULATE_DONE;
        }
 
-       if (kvm_read_guest(vcpu->kvm, pte.raddr, ptr, size))
+       vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+       rc = kvm_read_guest(vcpu->kvm, pte.raddr, ptr, size);
+       srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+       if (rc)
                return EMULATE_DO_MMIO;
 
        return EMULATE_DONE;