Re: [PATCH 3/8] KVM: arm64: Map AArch32 cp15 register to AArch64 sysregs

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 2020-11-03 18:29, James Morse wrote:
Hi Marc,

On 02/11/2020 19:16, Marc Zyngier wrote:
Move all the cp15 registers over to their AArch64 counterpart.
This requires the annotation of a few of them (such as the usual
DFAR/IFAR vs FAR_EL1), and a new helper that generates mask/shift
pairs for the various configurations.

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 26c7c25f8a6d..137818793a4a 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -138,26 +156,16 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
 			  const struct sys_reg_desc *r)
 {
 	bool was_enabled = vcpu_has_cache_enabled(vcpu);
-	u64 val;
-	int reg = r->reg;
+	u64 val, mask, shift;

 	BUG_ON(!p->is_write);

-	/* See the 32bit mapping in kvm_host.h */
-	if (p->is_aarch32)
-		reg = r->reg / 2;
+	get_access_mask(r, &mask, &shift);

-	if (!p->is_aarch32 || !p->is_32bit) {
-		val = p->regval;
-	} else {
-		val = vcpu_read_sys_reg(vcpu, reg);
-		if (r->reg % 2)
-			val = (p->regval << 32) | (u64)lower_32_bits(val);
-		else
-			val = ((u64)upper_32_bits(val) << 32) |
-				lower_32_bits(p->regval);
-	}
-	vcpu_write_sys_reg(vcpu, val, reg);

+	val = vcpu_read_sys_reg(vcpu, r->reg);
+	val &= ~mask;
+	val |= (p->regval & (mask >> shift)) << shift;
+	vcpu_write_sys_reg(vcpu, val, r->reg);

I can't tell if the compiler has worked out ithat it can skip the
sys_read most of the
time... Won't some of these trap for a nested VHE hypervisor?

| if (~mask) {
|	val = vcpu_read_sys_reg(vcpu, r->reg);
|	val &= ~mask;
| }

Seems like a good call. I'm happy to fold that in.



But, as the sys_reg arrays already have indirection for this function, why does
access_vm_reg() have to deal with this at all? Its not even needed for
all the aarch32 registers...


| { AA32(LO), Op1( 0), CRn(10), CRm( 2), Op2( 0),
access_aarch32_alias, NULL, MAIR_EL1 },

Where access_aarch32_alias() does the shift+mask and read_modify-write
on the sys_reg?


I don't really like the idea of separate handlers. The whole point is to
unify the two view, and I feel like having yet another indirection makes
it harder to maintain.


 	kvm_toggle_cache(vcpu, was_enabled);
 	return true;

@@ -1919,19 +1919,24 @@ static const struct sys_reg_desc cp14_64_regs[] = {
  */
 static const struct sys_reg_desc cp15_regs[] = {

- { Op1( 0), CRn( 2), CRm( 0), Op2( 2), access_vm_reg, NULL, c2_TTBCR },

+ { Op1( 0), CRn( 2), CRm( 0), Op2( 2), access_vm_reg, NULL, TCR_EL1 },

Don't look now ... TTBRCR2 means this one is a LO/HI job.

That's the problem with AArch32. You stop looking for a couple of years,
and it decides to throw a new sysreg at you without any notice. WTF?

(I'm guessing that should be fixed before this series to make the backport easy)

I'll work something out as a prologue to this series.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm



[Index of Archives]     [Linux KVM]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux