Re: [PATCH 4/4] KVM: x86: hyper-v: HVCALL_SEND_IPI_EX is an XMM fast hypercall

Siddharth Chandrasekaran
2022-02-28T10:48:56Z

On Tue, Feb 22, 2022 at 04:46:42PM +0100, Vitaly Kuznetsov wrote:
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> It has been proven on practice that at least Windows Server 2019 tries
> using HVCALL_SEND_IPI_EX in 'XMM fast' mode when it has more than 64 vCPUs
> and it needs to send an IPI to a vCPU > 63. Similarly to other XMM Fast
> hypercalls (HVCALL_FLUSH_VIRTUAL_ADDRESS_{LIST,SPACE}{,_EX}), this
> information is missing in TLFS as of 6.0b. Currently, KVM returns an error
> (HV_STATUS_INVALID_HYPERCALL_INPUT) and Windows crashes.
>
> Note, HVCALL_SEND_IPI is a 'standard' fast hypercall (not 'XMM fast') as
> all its parameters fit into RDX:R8 and this is handled by KVM correctly.
>
> Fixes: d8f5537a8816 ("KVM: hyper-v: Advertise support for fast XMM hypercalls")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

Reviewed-by: Siddharth Chandrasekaran <sidcha@amazon.de>

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