linux-kernel - Re: [PATCH 1/3] kvm: wire up KVM_CAP_VM_GPA

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Message-ID: <ZeWNdBSWVTAwtLyI@linux.bj.intel.com>
Date: Mon, 4 Mar 2024 16:59:32 +0800
From: Tao Su <tao1.su@...ux.intel.com>
To: Gerd Hoffmann <kraxel@...hat.com>
Cc: kvm@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] kvm: wire up KVM_CAP_VM_GPA_BITS for x86

On Mon, Mar 04, 2024 at 09:43:53AM +0100, Gerd Hoffmann wrote:
> > > +	kvm_caps.guest_phys_bits = boot_cpu_data.x86_phys_bits;
> > 
> > When KeyID_bits is non-zero, MAXPHYADDR != boot_cpu_data.x86_phys_bits
> > here, you can check in detect_tme().
> 
> from detect_tme():
> 
>         /*
>          * KeyID bits effectively lower the number of physical address
>          * bits.  Update cpuinfo_x86::x86_phys_bits accordingly.
>          */
>         c->x86_phys_bits -= keyid_bits;
> 
> This looks like x86_phys_bits gets adjusted if needed.

If TDP is enabled and supports 5-level, we want kvm_caps.guest_phys_bits=52,
but c->x86_phys_bits!=52 here. Maybe we need to set kvm_caps.guest_phys_bits
according to whether TDP is enabled or not, like leaf 0x80000008 in
__do_cpuid_func().

Thanks,
Tao