-----Original Message-----
From: Bae, Chang Seok <[email protected]>
Sent: Wednesday, December 23, 2020 11:57 PM
To: [email protected]; [email protected]; [email protected]; [email protected];
[email protected]
Cc: Brown, Len <[email protected]>; Hansen, Dave <[email protected]>;
Liu, Jing2 <[email protected]>; Shankar, Ravi V <[email protected]>;
[email protected]; Bae, Chang Seok <[email protected]>;
[email protected]
Subject: [PATCH v3 10/21] x86/fpu/xstate: Update xstate save function to
support dynamic xstate
copy_xregs_to_kernel() used to save all user states in a kernel buffer.
When the dynamic user state is enabled, it becomes conditional which state to
be saved.
fpu->state_mask can indicate which state components are reserved to be
saved in XSAVE buffer. Use it as XSAVE's instruction mask to select states.
KVM used to save all xstate via copy_xregs_to_kernel(). Update KVM to set a
valid fpu->state_mask, which will be necessary to correctly handle dynamic
state buffers.
See comments together below.
No functional change until the kernel supports dynamic user states.
Signed-off-by: Chang S. Bae <[email protected]>
Reviewed-by: Len Brown <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
[...]
/*
* AVX512 state is tracked here because its use is diff --git
a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 4aecfba04bd3..93b5bacad67a
100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9214,15 +9214,20 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
static void kvm_save_current_fpu(struct fpu *fpu) {
+ struct fpu *src_fpu = ¤t->thread.fpu;
+
/*
* If the target FPU state is not resident in the CPU registers, just
* memcpy() from current, else save CPU state directly to the target.
*/
- if (test_thread_flag(TIF_NEED_FPU_LOAD))
- memcpy(&fpu->state, ¤t->thread.fpu.state,
+ if (test_thread_flag(TIF_NEED_FPU_LOAD)) {
+ memcpy(&fpu->state, &src_fpu->state,
fpu_kernel_xstate_min_size);
For kvm, if we assume that it does not support dynamic features until this
series,
memcpy for only fpu->state is correct.
I think this kind of assumption is reasonable and we only make original xstate
work.
- else
+ } else {
+ if (fpu->state_mask != src_fpu->state_mask)
+ fpu->state_mask = src_fpu->state_mask;
Though dynamic feature is not supported in kvm now, this function still need
consider more things for fpu->state_mask.
I suggest that we can set it before if...else (for both cases) and not change
other.
Thanks,
Jing
copy_fpregs_to_fpstate(fpu);
+ }
}
/* Swap (qemu) user FPU context for the guest FPU context. */
--
2.17.1
