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Commit 4d8b81ab authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Avi Kivity
Browse files

KVM: introduce readonly memslot 



In current code, if we map a readonly memory space from host to guest
and the page is not currently mapped in the host, we will get a fault
pfn and async is not allowed, then the vm will crash

We introduce readonly memory region to map ROM/ROMD to the guest, read access
is happy for readonly memslot, write access on readonly memslot will cause
KVM_EXIT_MMIO exit

Signed-off-by: default avatarXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 7068d097

Documentation/virtual/kvm/api.txt

+7 −3
Original line number Diff line number Diff line
@@ -857,7 +857,8 @@ struct kvm_userspace_memory_region { 
};



/* for kvm_memory_region::flags */

#define KVM_MEM_LOG_DIRTY_PAGES  1UL

#define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)

#define KVM_MEM_READONLY	(1UL << 1)



This ioctl allows the user to create or modify a guest physical memory

slot.  When changing an existing slot, it may be moved in the guest
@@ -873,9 +874,12 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr 
be identical.  This allows large pages in the guest to be backed by large

pages in the host.



The flags field supports just one flag, KVM_MEM_LOG_DIRTY_PAGES, which

The flags field supports two flag, KVM_MEM_LOG_DIRTY_PAGES, which

instructs kvm to keep track of writes to memory within the slot.  See

the KVM_GET_DIRTY_LOG ioctl.

the KVM_GET_DIRTY_LOG ioctl. Another flag is KVM_MEM_READONLY when the

KVM_CAP_READONLY_MEM capability, it indicates the guest memory is read-only,

that means, guest is only allowed to read it. Writes will be posted to

userspace as KVM_EXIT_MMIO exits.



When the KVM_CAP_SYNC_MMU capability, changes in the backing of the memory

region are automatically reflected into the guest.  For example, an mmap()

arch/x86/include/asm/kvm.h

+1 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ 
#define __KVM_HAVE_DEBUGREGS

#define __KVM_HAVE_XSAVE

#define __KVM_HAVE_XCRS

#define __KVM_HAVE_READONLY_MEM



/* Architectural interrupt line count. */

#define KVM_NR_INTERRUPTS 256

arch/x86/kvm/mmu.c

+9 −0
Original line number Diff line number Diff line
@@ -2647,6 +2647,15 @@ static void kvm_send_hwpoison_signal(unsigned long address, struct task_struct * 


static int kvm_handle_bad_page(struct kvm_vcpu *vcpu, gfn_t gfn, pfn_t pfn)

{

	/*

	 * Do not cache the mmio info caused by writing the readonly gfn

	 * into the spte otherwise read access on readonly gfn also can

	 * caused mmio page fault and treat it as mmio access.

	 * Return 1 to tell kvm to emulate it.

	 */

	if (pfn == KVM_PFN_ERR_RO_FAULT)

		return 1;



	if (pfn == KVM_PFN_ERR_HWPOISON) {

		kvm_send_hwpoison_signal(gfn_to_hva(vcpu->kvm, gfn), current);

		return 0;

arch/x86/kvm/x86.c

+1 −0
Original line number Diff line number Diff line
@@ -2175,6 +2175,7 @@ int kvm_dev_ioctl_check_extension(long ext) 
	case KVM_CAP_GET_TSC_KHZ:

	case KVM_CAP_PCI_2_3:

	case KVM_CAP_KVMCLOCK_CTRL:

	case KVM_CAP_READONLY_MEM:

		r = 1;

		break;

	case KVM_CAP_COALESCED_MMIO:

include/linux/kvm.h

+5 −1
Original line number Diff line number Diff line
@@ -106,7 +106,8 @@ struct kvm_userspace_memory_region { 
 * other bits are reserved for kvm internal use which are defined in

 * include/linux/kvm_host.h.

 */

#define KVM_MEM_LOG_DIRTY_PAGES  1UL

#define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)

#define KVM_MEM_READONLY	(1UL << 1)



/* for KVM_IRQ_LINE */

struct kvm_irq_level {
@@ -621,6 +622,9 @@ struct kvm_ppc_smmu_info { 
#define KVM_CAP_PPC_GET_SMMU_INFO 78

#define KVM_CAP_S390_COW 79

#define KVM_CAP_PPC_ALLOC_HTAB 80

#ifdef __KVM_HAVE_READONLY_MEM

#define KVM_CAP_READONLY_MEM 81

#endif



#ifdef KVM_CAP_IRQ_ROUTING