[PATCH 8/8] KVM: SEV-ES: go over the sev_pio_data buffer in multiple passes if needed

Paolo Bonzini
2021-10-13T16:56:38Z

The PIO scratch buffer is larger than a single page, and therefore
it is not possible to copy it in a single step to vcpu->arch/pio_data.
Bound each call to emulator_pio_in/out to a single page; keep
track of how many I/O operations are left in vcpu->arch.sev_pio_count,
so that the operation can be restarted in the complete_userspace_io
callback.

For OUT, this means that the previous kvm_sev_es_outs implementation
becomes an iterator of the loop, and we can consume the sev_pio_data
buffer before leaving to userspace.

For IN, instead, consuming the buffer and decreasing sev_pio_count
is always done in the complete_userspace_io callback, because that
is when the memcpy is done into sev_pio_data.

Cc: stable@vger.kernel.org
Fixes: 7ed9abfe8e9f ("KVM: SVM: Support string IO operations for an SEV-ES guest")
Reported-by: Felix Wilhelm <fwilhelm@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/x86.c | 73 +++++++++++++++++++++++++--------
2 files changed, 57 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6bed6c416c6c..5a0298aa56ba 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -703,6 +703,7 @@ struct kvm_vcpu_arch {
struct kvm_pio_request pio;
void *pio_data;
void *sev_pio_data;
+ unsigned sev_pio_count;

u8 event_exit_inst_len;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a485e185ad00..09c1e64495d3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12378,38 +12378,76 @@ int kvm_sev_es_mmio_read(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned int bytes,
EXPORT_SYMBOL_GPL(kvm_sev_es_mmio_read);

static int kvm_sev_es_outs(struct kvm_vcpu *vcpu, unsigned int size,
- unsigned int port, unsigned int count)
+ unsigned int port);
+
+static int complete_sev_es_emulated_outs(struct kvm_vcpu *vcpu)
{
- int ret = emulator_pio_out(vcpu, size, port,
- vcpu->arch.sev_pio_data, count);
+ vcpu->arch.pio.count = 0;
+ if (vcpu->arch.sev_pio_count)
+ return kvm_sev_es_outs(vcpu,
+ vcpu->arch.pio.size,
+ vcpu->arch.pio.port);
+ return 1;
+}
+
+static int kvm_sev_es_outs(struct kvm_vcpu *vcpu, unsigned int size,
+ unsigned int port)
+{
+ for (;;) {
+ unsigned int count =
+ min_t(unsigned int, PAGE_SIZE / size, vcpu->arch.sev_pio_count);
+ int ret = emulator_pio_out(vcpu, size, port, vcpu->arch.sev_pio_data, count);
+
+ /* memcpy done already by emulator_pio_out. */
+ vcpu->arch.sev_pio_count -= count;
+ vcpu->arch.sev_pio_data += count * vcpu->arch.pio.size;
+ if (!ret)
+ break;

- if (ret) {
/* Emulation done by the kernel. */
- return ret;
+ vcpu->arch.pio.count = 0;
+ if (!vcpu->arch.sev_pio_count)
+ return 1;
}

- vcpu->arch.pio.count = 0;
+ vcpu->arch.complete_userspace_io = complete_sev_es_emulated_outs;
return 0;
}

-static int complete_sev_es_emulated_ins(struct kvm_vcpu *vcpu)
+static int kvm_sev_es_ins(struct kvm_vcpu *vcpu, unsigned int size,
+ unsigned int port);
+
+static void __complete_sev_es_emulated_ins(struct kvm_vcpu *vcpu)
{
- memcpy(vcpu->arch.sev_pio_data, vcpu->arch.pio_data,
- vcpu->arch.pio.count * vcpu->arch.pio.size);
- vcpu->arch.pio.count = 0;
+ unsigned count = vcpu->arch.pio.count;
+ complete_emulator_pio_in(vcpu, vcpu->arch.sev_pio_data);
+ vcpu->arch.sev_pio_count -= count;
+ vcpu->arch.sev_pio_data += count * vcpu->arch.pio.size;
+}

+static int complete_sev_es_emulated_ins(struct kvm_vcpu *vcpu)
+{
+ __complete_sev_es_emulated_ins(vcpu);
+ if (vcpu->arch.sev_pio_count)
+ return kvm_sev_es_ins(vcpu,
+ vcpu->arch.pio.size,
+ vcpu->arch.pio.port);
return 1;
}

static int kvm_sev_es_ins(struct kvm_vcpu *vcpu, unsigned int size,
- unsigned int port, unsigned int count)
+ unsigned int port)
{
- int ret = emulator_pio_in(vcpu, size, port,
- vcpu->arch.sev_pio_data, count);
+ for (;;) {
+ unsigned int count =
+ min_t(unsigned int, PAGE_SIZE / size, vcpu->arch.sev_pio_count);
+ if (!__emulator_pio_in(vcpu, size, port, count))
+ break;

- if (ret) {
/* Emulation done by the kernel. */
- return ret;
+ __complete_sev_es_emulated_ins(vcpu);
+ if (!vcpu->arch.sev_pio_count)
+ return 1;
}

vcpu->arch.complete_userspace_io = complete_sev_es_emulated_ins;
@@ -12421,8 +12459,9 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
int in)
{
vcpu->arch.sev_pio_data = data;
- return in ? kvm_sev_es_ins(vcpu, size, port, count)
- : kvm_sev_es_outs(vcpu, size, port, count);
+ vcpu->arch.sev_pio_count = count;
+ return in ? kvm_sev_es_ins(vcpu, size, port)
+ : kvm_sev_es_outs(vcpu, size, port);
}
EXPORT_SYMBOL_GPL(kvm_sev_es_string_io);

--
2.27.0