Commit 7d0a5e62 authored by Janosch Frank's avatar Janosch Frank Committed by Christian Borntraeger
Browse files

KVM: s390: Limit sthyi execution 



Store hypervisor information is a valid instruction not only in
supervisor state but also in problem state, i.e. the guest's
userspace. Its execution is not only computational and memory
intensive, but also has to get hold of the ipte lock to write to the
guest's memory.

This lock is not intended to be held often and long, especially not
from the untrusted guest userspace. Therefore we apply rate limiting
of sthyi executions per VM.

Signed-off-by: default avatarJanosch Frank <frankja@linux.vnet.ibm.com>
Acked-by: default avatarDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
parent 95ca2cb5

arch/s390/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -652,6 +652,7 @@ struct kvm_arch{ 
	wait_queue_head_t ipte_wq;

	int ipte_lock_count;

	struct mutex ipte_mutex;

	struct ratelimit_state sthyi_limit;

	spinlock_t start_stop_lock;

	struct sie_page2 *sie_page2;

	struct kvm_s390_cpu_model model;

arch/s390/kvm/kvm-s390.c

+2 −0
Original line number Diff line number Diff line
@@ -1151,6 +1151,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) 


	rc = -ENOMEM;



	ratelimit_state_init(&kvm->arch.sthyi_limit, 5 * HZ, 500);



	kvm->arch.use_esca = 0; /* start with basic SCA */

	rwlock_init(&kvm->arch.sca_lock);

	kvm->arch.sca = (struct bsca_block *) get_zeroed_page(GFP_KERNEL);

arch/s390/kvm/sthyi.c

+11 −0
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ 
#include <linux/errno.h>

#include <linux/pagemap.h>

#include <linux/vmalloc.h>

#include <linux/ratelimit.h>



#include <asm/kvm_host.h>

#include <asm/asm-offsets.h>
@@ -403,6 +404,16 @@ int handle_sthyi(struct kvm_vcpu *vcpu) 
	u64 code, addr, cc = 0;

	struct sthyi_sctns *sctns = NULL;



	/*

	 * STHYI requires extensive locking in the higher hypervisors

	 * and is very computational/memory expensive. Therefore we

	 * ratelimit the executions per VM.

	 */

	if (!__ratelimit(&vcpu->kvm->arch.sthyi_limit)) {

		kvm_s390_retry_instr(vcpu);

		return 0;

	}



	kvm_s390_get_regs_rre(vcpu, &reg1, &reg2);

	code = vcpu->run->s.regs.gprs[reg1];

	addr = vcpu->run->s.regs.gprs[reg2];

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