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KVM: nSVM: Add CLASS()es for automagically handling local kvm_vcpu_map() usage

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Add CLASS() definitions for locally mapping a PFN using kvm_vcpu_map()
given a vCPU+gfn pair.  In addition to eliminating the need to manually
do unmap(), e.g. in error paths, this will allow hardening KVM against
double-mapping without having to manually ensure every on-stack declaration
is zero-initialized.

Use "map local" as the primary terminology as the basic concept is more or
less the same as kmap_local(): ensure the current context has a kernel
mapping to the underlying memory.

Immediately convert the relatively straightforward nested SVM flows, and
defer converting the more involved SMM flows to a separate change.

No functional change intended.

Cc: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260724004757.131420-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2026-07-23 17:47:53 -07:00
parent 11722439fb
commit d196e4d91e
3 changed files with 29 additions and 16 deletions
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18
arch/x86/kvm/svm/nested.c
View File

@ -1086,14 +1086,14 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa, bool from_vmrun)
static int nested_svm_copy_vmcb12_to_cache(struct kvm_vcpu *vcpu, u64 vmcb12_gpa)
{
struct vcpu_svm *svm = to_svm(vcpu);
struct kvm_host_map map;
struct vmcb *vmcb12;
int r = 0;
if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map))
CLASS(kvm_vcpu_map_local, m)(vcpu, gpa_to_gfn(vmcb12_gpa));
if (m.ret)
return -EFAULT;
vmcb12 = map.hva;
vmcb12 = m.map.hva;
nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
@ -1107,7 +1107,6 @@ static int nested_svm_copy_vmcb12_to_cache(struct kvm_vcpu *vcpu, u64 vmcb12_gpa
r = -EINVAL;
}
kvm_vcpu_unmap(vcpu, &map);
return r;
}
@ -1251,15 +1250,13 @@ static int nested_svm_vmexit_update_vmcb12(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
struct kvm_host_map map;
struct vmcb *vmcb12;
int rc;
rc = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map);
if (rc)
return rc;
CLASS(kvm_vcpu_map_local, m)(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa));
if (m.ret)
return m.ret;
vmcb12 = map.hva;
vmcb12 = m.map.hva;
vmcb12->save.es = vmcb02->save.es;
vmcb12->save.cs = vmcb02->save.cs;
@ -1314,7 +1311,6 @@ static int nested_svm_vmexit_update_vmcb12(struct kvm_vcpu *vcpu)
vmcb12->control.exit_int_info_err,
KVM_ISA_SVM);
kvm_vcpu_unmap(vcpu, &map);
return 0;
}

8
arch/x86/kvm/svm/svm.c
View File

@ -2221,7 +2221,6 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
u64 vmcb12_gpa = kvm_rax_read(vcpu);
struct vcpu_svm *svm = to_svm(vcpu);
struct vmcb *vmcb12;
struct kvm_host_map map;
int ret;
if (nested_svm_check_permissions(vcpu))
@ -2232,10 +2231,11 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
return 1;
}
if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map))
CLASS(kvm_vcpu_map_local, m)(vcpu, gpa_to_gfn(vmcb12_gpa));
if (m.ret)
return kvm_handle_memory_failure(vcpu, X86EMUL_IO_NEEDED, NULL);
vmcb12 = map.hva;
vmcb12 = m.map.hva;
ret = kvm_skip_emulated_instruction(vcpu);
@ -2248,8 +2248,6 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
svm_copy_vmloadsave_state(vmcb12, svm->vmcb01.ptr);
}
kvm_vcpu_unmap(vcpu, &map);
return ret;
}

19
include/linux/kvm_host.h
View File

@ -1420,6 +1420,25 @@ static inline void kvm_vcpu_map_mark_dirty(struct kvm_vcpu *vcpu,
kvm_vcpu_mark_page_dirty(vcpu, map->gfn);
}
typedef struct {
struct kvm_vcpu *vcpu;
struct kvm_host_map map;
int ret;
} kvm_vcpu_local_map_t;
#define DEFINE_VCPU_MAP_CLASS(ro) \
DEFINE_CLASS(kvm_vcpu_map_local##ro, kvm_vcpu_local_map_t, \
if (!_T.ret) kvm_vcpu_unmap(_T.vcpu, &_T.map), \
({ \
kvm_vcpu_local_map_t m = { .vcpu = vcpu }; \
\
m.ret = kvm_vcpu_map##ro(vcpu, gfn, &m.map); \
\
m; \
}), struct kvm_vcpu *vcpu, gfn_t gfn);
DEFINE_VCPU_MAP_CLASS();
DEFINE_VCPU_MAP_CLASS(_readonly);
unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn);
unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable);
int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset,