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Subject[RFC PATCH 18/35] KVM: SVM: Support MMIO for an SEV-ES guest
Date
From: Tom Lendacky <thomas.lendacky@amd.com>

For an SEV-ES guest, MMIO is performed to a shared (un-encrypted) page
so that both the hypervisor and guest can read or write to it and each
see the contents.

The GHCB specification provides software-defined VMGEXIT exit codes to
indicate a request for an MMIO read or an MMIO write. Add support to
recognize the MMIO requests and invoke SEV-ES specific routines that
can complete the MMIO operation. These routines use common KVM support
to complete the MMIO operation.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/kvm/svm/sev.c | 116 ++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.c | 3 +
arch/x86/kvm/svm/svm.h | 6 ++
arch/x86/kvm/x86.c | 123 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.h | 5 ++
5 files changed, 253 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 92a4df26057a..740b44485f36 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1191,6 +1191,24 @@ static void pre_sev_es_run(struct vcpu_svm *svm)
if (!svm->ghcb)
return;

+ if (svm->ghcb_sa_free) {
+ /*
+ * The scratch area lives outside the GHCB, so there is a
+ * buffer that, depending on the operation performed, may
+ * need to be synced, then freed.
+ */
+ if (svm->ghcb_sa_sync) {
+ kvm_write_guest(svm->vcpu.kvm,
+ ghcb_get_sw_scratch(svm->ghcb),
+ svm->ghcb_sa, svm->ghcb_sa_len);
+ svm->ghcb_sa_sync = false;
+ }
+
+ kfree(svm->ghcb_sa);
+ svm->ghcb_sa = NULL;
+ svm->ghcb_sa_free = false;
+ }
+
trace_kvm_vmgexit_exit(svm->vcpu.vcpu_id, svm->ghcb);

kvm_vcpu_unmap(&svm->vcpu, &svm->ghcb_map, true);
@@ -1223,6 +1241,86 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu)
vmcb_mark_dirty(svm->vmcb, VMCB_ASID);
}

+#define GHCB_SCRATCH_AREA_LIMIT (16ULL * PAGE_SIZE)
+static bool setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
+{
+ struct vmcb_control_area *control = &svm->vmcb->control;
+ struct ghcb *ghcb = svm->ghcb;
+ u64 ghcb_scratch_beg, ghcb_scratch_end;
+ u64 scratch_gpa_beg, scratch_gpa_end;
+ void *scratch_va;
+
+ scratch_gpa_beg = ghcb_get_sw_scratch(ghcb);
+ if (!scratch_gpa_beg) {
+ pr_err("vmgexit: scratch gpa not provided\n");
+ return false;
+ }
+
+ scratch_gpa_end = scratch_gpa_beg + len;
+ if (scratch_gpa_end < scratch_gpa_beg) {
+ pr_err("vmgexit: scratch length (%#llx) not valid for scratch address (%#llx)\n",
+ len, scratch_gpa_beg);
+ return false;
+ }
+
+ if ((scratch_gpa_beg & PAGE_MASK) == control->ghcb_gpa) {
+ /* Scratch area begins within GHCB */
+ ghcb_scratch_beg = control->ghcb_gpa +
+ offsetof(struct ghcb, shared_buffer);
+ ghcb_scratch_end = control->ghcb_gpa +
+ offsetof(struct ghcb, reserved_1);
+
+ /*
+ * If the scratch area begins within the GHCB, it must be
+ * completely contained in the GHCB shared buffer area.
+ */
+ if (scratch_gpa_beg < ghcb_scratch_beg ||
+ scratch_gpa_end > ghcb_scratch_end) {
+ pr_err("vmgexit: scratch area is outside of GHCB shared buffer area (%#llx - %#llx)\n",
+ scratch_gpa_beg, scratch_gpa_end);
+ return false;
+ }
+
+ scratch_va = (void *)svm->ghcb;
+ scratch_va += (scratch_gpa_beg - control->ghcb_gpa);
+ } else {
+ /*
+ * The guest memory must be read into a kernel buffer, so
+ * limit the size
+ */
+ if (len > GHCB_SCRATCH_AREA_LIMIT) {
+ pr_err("vmgexit: scratch area exceeds KVM limits (%#llx requested, %#llx limit)\n",
+ len, GHCB_SCRATCH_AREA_LIMIT);
+ return false;
+ }
+ scratch_va = kzalloc(len, GFP_KERNEL);
+ if (!scratch_va)
+ return false;
+
+ if (kvm_read_guest(svm->vcpu.kvm, scratch_gpa_beg, scratch_va, len)) {
+ /* Unable to copy scratch area from guest */
+ pr_err("vmgexit: kvm_read_guest for scratch area failed\n");
+
+ kfree(scratch_va);
+ return false;
+ }
+
+ /*
+ * The scratch area is outside the GHCB. The operation will
+ * dictate whether the buffer needs to be synced before running
+ * the vCPU next time (i.e. a read was requested so the data
+ * must be written back to the guest memory).
+ */
+ svm->ghcb_sa_sync = sync;
+ svm->ghcb_sa_free = true;
+ }
+
+ svm->ghcb_sa = scratch_va;
+ svm->ghcb_sa_len = len;
+
+ return true;
+}
+
static void set_ghcb_msr_bits(struct vcpu_svm *svm, u64 value, u64 mask,
unsigned int pos)
{
@@ -1356,6 +1454,24 @@ int sev_handle_vmgexit(struct vcpu_svm *svm)

ret = -EINVAL;
switch (ghcb_get_sw_exit_code(ghcb)) {
+ case SVM_VMGEXIT_MMIO_READ:
+ if (!setup_vmgexit_scratch(svm, true, control->exit_info_2))
+ break;
+
+ ret = kvm_sev_es_mmio_read(&svm->vcpu,
+ control->exit_info_1,
+ control->exit_info_2,
+ svm->ghcb_sa);
+ break;
+ case SVM_VMGEXIT_MMIO_WRITE:
+ if (!setup_vmgexit_scratch(svm, false, control->exit_info_2))
+ break;
+
+ ret = kvm_sev_es_mmio_write(&svm->vcpu,
+ control->exit_info_1,
+ control->exit_info_2,
+ svm->ghcb_sa);
+ break;
case SVM_VMGEXIT_UNSUPPORTED_EVENT:
pr_err("vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
control->exit_info_1,
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 89ee9d533e9a..439b0d0e53eb 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1306,6 +1306,9 @@ static void svm_free_vcpu(struct kvm_vcpu *vcpu)
}

__free_page(virt_to_page(svm->vmsa));
+
+ if (svm->ghcb_sa_free)
+ kfree(svm->ghcb_sa);
}

__free_page(pfn_to_page(__sme_clr(svm->vmcb_pa) >> PAGE_SHIFT));
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 3574f52f8a1c..8de45462ff4a 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -165,6 +165,12 @@ struct vcpu_svm {
struct vmcb_save_area *vmsa;
struct ghcb *ghcb;
struct kvm_host_map ghcb_map;
+
+ /* SEV-ES scratch area support */
+ void *ghcb_sa;
+ u64 ghcb_sa_len;
+ bool ghcb_sa_sync;
+ bool ghcb_sa_free;
};

struct svm_cpu_data {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2a2a394126a2..a0070eeeb139 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10768,6 +10768,129 @@ void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_c
}
EXPORT_SYMBOL_GPL(kvm_fixup_and_inject_pf_error);

+static int complete_sev_es_emulated_mmio(struct kvm_vcpu *vcpu)
+{
+ struct kvm_run *run = vcpu->run;
+ struct kvm_mmio_fragment *frag;
+ unsigned int len;
+
+ BUG_ON(!vcpu->mmio_needed);
+
+ /* Complete previous fragment */
+ frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment];
+ len = min(8u, frag->len);
+ if (!vcpu->mmio_is_write)
+ memcpy(frag->data, run->mmio.data, len);
+
+ if (frag->len <= 8) {
+ /* Switch to the next fragment. */
+ frag++;
+ vcpu->mmio_cur_fragment++;
+ } else {
+ /* Go forward to the next mmio piece. */
+ frag->data += len;
+ frag->gpa += len;
+ frag->len -= len;
+ }
+
+ if (vcpu->mmio_cur_fragment >= vcpu->mmio_nr_fragments) {
+ vcpu->mmio_needed = 0;
+
+ // VMG change, at this point, we're always done
+ // RIP has already been advanced
+ return 1;
+ }
+
+ // More MMIO is needed
+ run->mmio.phys_addr = frag->gpa;
+ run->mmio.len = min(8u, frag->len);
+ run->mmio.is_write = vcpu->mmio_is_write;
+ if (run->mmio.is_write)
+ memcpy(run->mmio.data, frag->data, min(8u, frag->len));
+ run->exit_reason = KVM_EXIT_MMIO;
+
+ vcpu->arch.complete_userspace_io = complete_sev_es_emulated_mmio;
+
+ return 0;
+}
+
+int kvm_sev_es_mmio_write(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned int bytes,
+ void *data)
+{
+ int handled;
+ struct kvm_mmio_fragment *frag;
+
+ if (!data)
+ return -EINVAL;
+
+ handled = write_emultor.read_write_mmio(vcpu, gpa, bytes, data);
+ if (handled == bytes)
+ return 1;
+
+ bytes -= handled;
+ gpa += handled;
+ data += handled;
+
+ /*TODO: Check if need to increment number of frags */
+ frag = vcpu->mmio_fragments;
+ vcpu->mmio_nr_fragments = 1;
+ frag->len = bytes;
+ frag->gpa = gpa;
+ frag->data = data;
+
+ vcpu->mmio_needed = 1;
+ vcpu->mmio_cur_fragment = 0;
+
+ vcpu->run->mmio.phys_addr = gpa;
+ vcpu->run->mmio.len = min(8u, frag->len);
+ vcpu->run->mmio.is_write = 1;
+ memcpy(vcpu->run->mmio.data, frag->data, min(8u, frag->len));
+ vcpu->run->exit_reason = KVM_EXIT_MMIO;
+
+ vcpu->arch.complete_userspace_io = complete_sev_es_emulated_mmio;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_sev_es_mmio_write);
+
+int kvm_sev_es_mmio_read(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned int bytes,
+ void *data)
+{
+ int handled;
+ struct kvm_mmio_fragment *frag;
+
+ if (!data)
+ return -EINVAL;
+
+ handled = read_emultor.read_write_mmio(vcpu, gpa, bytes, data);
+ if (handled == bytes)
+ return 1;
+
+ bytes -= handled;
+ gpa += handled;
+ data += handled;
+
+ /*TODO: Check if need to increment number of frags */
+ frag = vcpu->mmio_fragments;
+ vcpu->mmio_nr_fragments = 1;
+ frag->len = bytes;
+ frag->gpa = gpa;
+ frag->data = data;
+
+ vcpu->mmio_needed = 1;
+ vcpu->mmio_cur_fragment = 0;
+
+ vcpu->run->mmio.phys_addr = gpa;
+ vcpu->run->mmio.len = min(8u, frag->len);
+ vcpu->run->mmio.is_write = 0;
+ vcpu->run->exit_reason = KVM_EXIT_MMIO;
+
+ vcpu->arch.complete_userspace_io = complete_sev_es_emulated_mmio;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_sev_es_mmio_read);
+
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 995ab696dcf0..ce3b7d3d8631 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -398,4 +398,9 @@ bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu);
__reserved_bits; \
})

+int kvm_sev_es_mmio_write(struct kvm_vcpu *vcpu, gpa_t src, unsigned int bytes,
+ void *dst);
+int kvm_sev_es_mmio_read(struct kvm_vcpu *vcpu, gpa_t src, unsigned int bytes,
+ void *dst);
+
#endif
--
2.28.0
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