Re: [PATCH 01/11] KVM: arm64: Store vcpu on the stack during __guest_enter()

On Tue, Aug 08, 2017 at 05:48:29PM +0100, James Morse wrote:

Hi Christoffer,

On 06/06/17 20:59, Christoffer Dall wrote:

quoted

On Mon, May 15, 2017 at 06:43:49PM +0100, James Morse wrote:

quoted

KVM uses tpidr_el2 as its private vcpu register, which makes sense for
non-vhe world switch as only KVM can access this register. This means
vhe Linux has to use tpidr_el1, which KVM has to save/restore as part
of the host context.

__guest_enter() stores the host_ctxt on the stack, do the same with
the vcpu.

quoted

quoted

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 12ee62d6d410..113735df7d01 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S

@@ -159,9 +159,15 @@ abort_guest_exit_end:
 ENDPROC(__guest_exit)
 
 ENTRY(__fpsimd_guest_restore)
+	// x0: esr
+	// x1: vcpu
+	// x2-x29,lr: vcpu regs
+	// vcpu x0-x1 on the stack
 	stp	x2, x3, [sp, #-16]!
 	stp	x4, lr, [sp, #-16]!
 
+	mov	x3, x1
+

nit: can you avoid this by using x1 for the vcpu pointer in this routine
instead?

Unfortunately x1 is clobbered by the __fpsimd_{save,restore}_state() macros that
are called further down this function.

(its a bit obscure:

quoted

fpsimd_save	x0, 1

that '1' is used to generate 'x1' or 'w1' in includes/asm/fpsimdmacros.h)

Ah, I guess I missed that.

Thanks,
-Christoffer
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