linux-kernel - Re: [External] Re: [PATCH v2] RISC-V: KVM: Delegate kvm unhandled faults to VS mode

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Message-ID: <CAPYmKFu2Ggu7_SFkrhfKX9rT7Pdas+jSjksGMFAhHf7Wa83Y8g@mail.gmail.com>
Date: Fri, 11 Jul 2025 16:25:48 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: Radim Krčmář <rkrcmar@...tanamicro.com>
Cc: cleger@...osinc.com, anup@...infault.org, atish.patra@...ux.dev, 
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, 
	alex@...ti.fr, kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v2] RISC-V: KVM: Delegate kvm unhandled
 faults to VS mode

On Fri, Jul 11, 2025 at 2:16 PM Radim Krčmář <rkrcmar@...tanamicro.com> wrote:
>
> 2025-07-10T21:30:30+08:00, Xu Lu <luxu.kernel@...edance.com>:
> > Delegate faults which are not handled by kvm to VS mode to avoid
> > unnecessary traps to HS mode. These faults include illegal instruction
> > fault, instruction access fault, load access fault and store access
> > fault.
> >
> > The delegation of illegal instruction fault is particularly important
> > to guest applications that use vector instructions frequently. In such
> > cases, an illegal instruction fault will be raised when guest user thread
> > uses vector instruction the first time and then guest kernel will enable
> > user thread to execute following vector instructions.
>
> (This optimization will be even more significant when nesting, where it
>  would currently go -> HS0 -> HS1 -> HS0 -> VS1, instead of -> VS1.)

Nice supplement! Thanks.

>
> > The fw pmu event counters remain undeleted so that guest can still get
> > these events via sbi call. Guest will only see zero count on these
> > events and know 'firmware' has delegated these faults.
> >
> > Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
> > ---
>
> Reviewed-by: Radim Krčmář <rkrcmar@...tanamicro.com>