On 18/04/2023 11:48, Paul Durrant wrote:
>On 18/04/2023 11:13, Metin Kaya wrote:
>> Implement in-KVM support for Xen's HVMOP_flush_tlbs hypercall, which
>> allows the guest to flush all vCPU's TLBs. KVM doesn't provide an
>> ioctl() to precisely flush guest TLBs, and punting to userspace would
>> likely negate the performance benefits of avoiding a TLB shootdown in
>> the guest.
>>
>> Signed-off-by: Metin Kaya <metikaya@xxxxxxxxxxxx>
>>
>> ---
>> v3:
>> - Addressed comments for v2.
>> - Verified with XTF/invlpg test case.
>>
>> v2:
>> - Removed an irrelevant URL from commit message.
>> ---
>> arch/x86/kvm/xen.c | 15 +++++++++++++++
>> include/xen/interface/hvm/hvm_op.h | 3 +++
>> 2 files changed, 18 insertions(+)
>>
>> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index
>> 40edf4d1974c..a63c48e8d8fa 100644
>> --- a/arch/x86/kvm/xen.c
>> +++ b/arch/x86/kvm/xen.c
>> @@ -21,6 +21,7 @@
>> #include <xen/interface/vcpu.h>
>> #include <xen/interface/version.h>
>> #include <xen/interface/event_channel.h>
>> +#include <xen/interface/hvm/hvm_op.h>
>> #include <xen/interface/sched.h>
>>
>> #include <asm/xen/cpuid.h>
>> @@ -1330,6 +1331,17 @@ static bool kvm_xen_hcall_sched_op(struct kvm_vcpu *vcpu, bool longmode,
>> return false;
>> }
>>
>> +static bool kvm_xen_hcall_hvm_op(struct kvm_vcpu *vcpu, int cmd, u64
>> +arg, u64 *r) {
>> + if (cmd == HVMOP_flush_tlbs && !arg) {
>> + kvm_make_all_cpus_request(vcpu->kvm, KVM_REQ_TLB_FLUSH_GUEST);
>> + *r = 0;
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>
>This code structure means that arg != NULL will result in the guest seeing ENOSYS rather than EINVAL.
>
> Paul
Yes, because of this comment in David's email:
"I don't even know that we care about in-kernel acceleration for the
-EINVAL case. We could just return false for that, and let userspace
(report and) handle it."
>
>> +
>> struct compat_vcpu_set_singleshot_timer {
>> uint64_t timeout_abs_ns;
>> uint32_t flags;
>> @@ -1501,6 +1513,9 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
>> timeout |= params[1] << 32;
>> handled = kvm_xen_hcall_set_timer_op(vcpu, timeout, &r);
>> break;
>> + case __HYPERVISOR_hvm_op:
>> + handled = kvm_xen_hcall_hvm_op(vcpu, params[0], params[1], &r);
>> + break;
>> }
>> default:
>> break;
>> diff --git a/include/xen/interface/hvm/hvm_op.h
>> b/include/xen/interface/hvm/hvm_op.h
>> index 03134bf3cec1..240d8149bc04 100644
>> --- a/include/xen/interface/hvm/hvm_op.h
>> +++ b/include/xen/interface/hvm/hvm_op.h
>> @@ -16,6 +16,9 @@ struct xen_hvm_param {
>> };
>> DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_param);
>>
>> +/* Flushes guest TLBs for all vCPUs: @arg must be 0. */
>> +#define HVMOP_flush_tlbs 5
>> +
>> /* Hint from PV drivers for pagetable destruction. */
>> #define HVMOP_pagetable_dying 9
>> struct xen_hvm_pagetable_dying {
>
