linux-kernel - Re: [PATCH 4/4] arm64/sysreg: Add VTCR

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Message-ID: <87sehnk8ud.wl-maz@kernel.org>
Date: Tue, 19 Aug 2025 09:35:06 +0100
From: Marc Zyngier <maz@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Mark Brown <broonie@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] arm64/sysreg: Add VTCR_EL2 register

On Tue, 19 Aug 2025 05:24:29 +0100,
Anshuman Khandual <anshuman.khandual@....com> wrote:
> 
> 
> 
> On 18/08/25 2:52 PM, Mark Rutland wrote:
> > On Mon, Aug 18, 2025 at 10:27:59AM +0530, Anshuman Khandual wrote:
> >> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> >> index d2b40105eb41..f5a0a304f844 100644
> >> --- a/arch/arm64/tools/sysreg
> >> +++ b/arch/arm64/tools/sysreg
> >> @@ -4910,6 +4910,63 @@ Field	1	PIE
> >>  Field	0	PnCH
> >>  EndSysreg
> >>  
> >> +Sysreg	VTCR_EL2	3	4	2	1	2
> >> +Res0	63:46
> >> +Field	45	HDBSS
> >> +Field	44	HAFT
> >> +Res0	43:42
> >> +Field	41	TL0
> >> +Field	40	GCSH
> >> +Res0	39
> >> +Field	38	D128
> >> +Field	37	S2POE
> >> +Field	36	S2PIE
> >> +Field	35	TL1
> >> +Field	34	AssuredOnly
> >> +Field	33	SL2
> >> +Field	32	DS
> >> +Res1	31
> >> +Field	30	NSA
> >> +Field	29	NSW
> >> +Field	28	HWU62
> >> +Field	27	HWU61
> >> +Field	26	HWU60
> >> +Field	25	HWU59
> >> +Res0	24:23
> >> +Field	22	HD
> >> +Field	21	HA
> >> +Res0	20
> >> +UnsignedEnum	19	VS
> >> +	0b0	8BIT
> >> +	0b1	16BIT
> >> +EndEnum
> > 
> > You left TCR_EL1.AS as a single-bit 'Field', so please do the same here
> > for consistency. I don't think there's much gained by making this any
> > sort of enum.
> 
> But actually there is an use case in kvm_get_vtcr().
> 
>         /* Set the vmid bits */
>         vtcr |= (get_vmid_bits(mmfr1) == 16) ?
>                 SYS_FIELD_PREP_ENUM(VTCR_EL2, VS, 16BIT) :
>                 SYS_FIELD_PREP_ENUM(VTCR_EL2, VS, 8BIT);
>

Here you go (untested):

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index c351b4abd5db..49266efc8bab 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -623,10 +623,7 @@ u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
 	if (kvm_lpa2_is_enabled())
 		vtcr |= VTCR_EL2_DS;
 
-	/* Set the vmid bits */
-	vtcr |= (get_vmid_bits(mmfr1) == 16) ?
-		VTCR_EL2_VS_16BIT :
-		VTCR_EL2_VS_8BIT;
+	vtcr |= FIELD_PREP(BIT(VTCR_EL2_VS_SHIFT), (get_vmid_bits(mmfr1) == 16));
 
 	return vtcr;
 }

	M.

-- 
Jazz isn't dead. It just smells funny.