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Commit 54738c09 authored by David Gibson's avatar David Gibson Committed by Avi Kivity
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KVM: PPC: Accelerate H_PUT_TCE by implementing it in real mode 



This improves I/O performance for guests using the PAPR
paravirtualization interface by making the H_PUT_TCE hcall faster, by
implementing it in real mode.  H_PUT_TCE is used for updating virtual
IOMMU tables, and is used both for virtual I/O and for real I/O in the
PAPR interface.

Since this moves the IOMMU tables into the kernel, we define a new
KVM_CREATE_SPAPR_TCE ioctl to allow qemu to create the tables.  The
ioctl returns a file descriptor which can be used to mmap the newly
created table.  The qemu driver models use them in the same way as
userspace managed tables, but they can be updated directly by the
guest with a real-mode H_PUT_TCE implementation, reducing the number
of host/guest context switches during guest IO.

There are certain circumstances where it is useful for userland qemu
to write to the TCE table even if the kernel H_PUT_TCE path is used
most of the time.  Specifically, allowing this will avoid awkwardness
when we need to reset the table.  More importantly, we will in the
future need to write the table in order to restore its state after a
checkpoint resume or migration.

Signed-off-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
parent a8606e20

Documentation/virtual/kvm/api.txt

+35 −0
Original line number Diff line number Diff line
@@ -1350,6 +1350,41 @@ The following flags are defined: 
If datamatch flag is set, the event will be signaled only if the written value

to the registered address is equal to datamatch in struct kvm_ioeventfd.



4.62 KVM_CREATE_SPAPR_TCE



Capability: KVM_CAP_SPAPR_TCE

Architectures: powerpc

Type: vm ioctl

Parameters: struct kvm_create_spapr_tce (in)

Returns: file descriptor for manipulating the created TCE table



This creates a virtual TCE (translation control entry) table, which

is an IOMMU for PAPR-style virtual I/O.  It is used to translate

logical addresses used in virtual I/O into guest physical addresses,

and provides a scatter/gather capability for PAPR virtual I/O.



/* for KVM_CAP_SPAPR_TCE */

struct kvm_create_spapr_tce {

	__u64 liobn;

	__u32 window_size;

};



The liobn field gives the logical IO bus number for which to create a

TCE table.  The window_size field specifies the size of the DMA window

which this TCE table will translate - the table will contain one 64

bit TCE entry for every 4kiB of the DMA window.



When the guest issues an H_PUT_TCE hcall on a liobn for which a TCE

table has been created using this ioctl(), the kernel will handle it

in real mode, updating the TCE table.  H_PUT_TCE calls for other

liobns will cause a vm exit and must be handled by userspace.



The return value is a file descriptor which can be passed to mmap(2)

to map the created TCE table into userspace.  This lets userspace read

the entries written by kernel-handled H_PUT_TCE calls, and also lets

userspace update the TCE table directly which is useful in some

circumstances.



5. The kvm_run structure



Application code obtains a pointer to the kvm_run structure by

arch/powerpc/include/asm/kvm.h

+9 −0
Original line number Diff line number Diff line
@@ -22,6 +22,9 @@ 


#include <linux/types.h>



/* Select powerpc specific features in <linux/kvm.h> */

#define __KVM_HAVE_SPAPR_TCE



struct kvm_regs {

	__u64 pc;

	__u64 cr;
@@ -272,4 +275,10 @@ struct kvm_guest_debug_arch { 
#define KVM_INTERRUPT_UNSET	-2U

#define KVM_INTERRUPT_SET_LEVEL	-3U



/* for KVM_CAP_SPAPR_TCE */

struct kvm_create_spapr_tce {

	__u64 liobn;

	__u32 window_size;

};



#endif /* __LINUX_KVM_POWERPC_H */

arch/powerpc/include/asm/kvm_book3s_64.h

+2 −0
Original line number Diff line number Diff line
@@ -27,4 +27,6 @@ static inline struct kvmppc_book3s_shadow_vcpu *to_svcpu(struct kvm_vcpu *vcpu) 
}

#endif



#define SPAPR_TCE_SHIFT		12



#endif /* __ASM_KVM_BOOK3S_64_H__ */

arch/powerpc/include/asm/kvm_host.h

+9 −0
Original line number Diff line number Diff line
@@ -144,6 +144,14 @@ struct kvmppc_pginfo { 
	atomic_t refcnt;

};



struct kvmppc_spapr_tce_table {

	struct list_head list;

	struct kvm *kvm;

	u64 liobn;

	u32 window_size;

	struct page *pages[0];

};



struct kvm_arch {

#ifdef CONFIG_KVM_BOOK3S_64_HV

	unsigned long hpt_virt;
@@ -157,6 +165,7 @@ struct kvm_arch { 
	unsigned long sdr1;

	unsigned long host_sdr1;

	int tlbie_lock;

	struct list_head spapr_tce_tables;

	unsigned short last_vcpu[NR_CPUS];

#endif /* CONFIG_KVM_BOOK3S_64_HV */

};

arch/powerpc/include/asm/kvm_ppc.h

+2 −0
Original line number Diff line number Diff line
@@ -119,6 +119,8 @@ extern long kvmppc_prepare_vrma(struct kvm *kvm, 
extern void kvmppc_map_vrma(struct kvm *kvm,

			    struct kvm_userspace_memory_region *mem);

extern int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu);

extern long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,

				struct kvm_create_spapr_tce *args);

extern int kvmppc_core_init_vm(struct kvm *kvm);

extern void kvmppc_core_destroy_vm(struct kvm *kvm);

extern int kvmppc_core_prepare_memory_region(struct kvm *kvm,