On Fri, Aug 18, 2023 at 05:50:28AM -0400,
Xiaoyao Li wrote:
> From: Isaku Yamahata
>
> If the range for TDG.VP.VMCALL is too large, process the limited
> size and return retry error. It's bad for VMM to take too long time,
> e.g. second order, with blocking vcpu execution. It results in too many
> missing timer interrupts.
This patch requires the guest side patch. [1]
Unless with large guest memory, it's unlikely to hit the limit with KVM/qemu,
though.
[1] https://lore.kernel.org/all/20230811021246.821-1-de...@microsoft.com/
>
> Signed-off-by: Isaku Yamahata
> Signed-off-by: Xiaoyao Li
> ---
> target/i386/kvm/tdx.c | 19 ++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> index 0c43c1f7759f..ced55be506d1 100644
> --- a/target/i386/kvm/tdx.c
> +++ b/target/i386/kvm/tdx.c
> @@ -994,12 +994,16 @@ static hwaddr tdx_shared_bit(X86CPU *cpu)
> return (cpu->phys_bits > 48) ? BIT_ULL(51) : BIT_ULL(47);
> }
>
> +/* 64MB at most in one call. What value is appropriate? */
> +#define TDX_MAP_GPA_MAX_LEN (64 * 1024 * 1024)
> +
> static void tdx_handle_map_gpa(X86CPU *cpu, struct kvm_tdx_vmcall *vmcall)
> {
> hwaddr shared_bit = tdx_shared_bit(cpu);
> hwaddr gpa = vmcall->in_r12 & ~shared_bit;
> bool private = !(vmcall->in_r12 & shared_bit);
> hwaddr size = vmcall->in_r13;
> +bool retry = false;
> int ret = 0;
>
> vmcall->status_code = TDG_VP_VMCALL_INVALID_OPERAND;
> @@ -1018,12 +1022,25 @@ static void tdx_handle_map_gpa(X86CPU *cpu, struct
> kvm_tdx_vmcall *vmcall)
> return;
> }
>
> +if (size > TDX_MAP_GPA_MAX_LEN) {
> +retry = true;
> +size = TDX_MAP_GPA_MAX_LEN;
> +}
> +
> if (size > 0) {
> ret = kvm_convert_memory(gpa, size, private);
> }
>
> if (!ret) {
> -vmcall->status_code = TDG_VP_VMCALL_SUCCESS;
> +if (retry) {
> +vmcall->status_code = TDG_VP_VMCALL_RETRY;
> +vmcall->out_r11 = gpa + size;
> +if (!private) {
> +vmcall->out_r11 |= shared_bit;
> +}
> +} else {
> +vmcall->status_code = TDG_VP_VMCALL_SUCCESS;
> +}
> }
> }
>
> --
> 2.34.1
>
>
--
Isaku Yamahata
