linux-kernel - Re: [CFT PATCH 0/2] KVM: support XSAVES usage in the host

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Message-Id: <DAC65E0B-06CC-4B34-85B2-72AD5F86826B@gmail.com>
Date:	Mon, 24 Nov 2014 17:28:41 +0200
From:	Nadav Amit <nadav.amit@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Nadav Amit <namit@...technion.ac.il>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [CFT PATCH 0/2] KVM: support XSAVES usage in the host


> On Nov 24, 2014, at 13:39, Paolo Bonzini <pbonzini@...hat.com> wrote:
> 
> 
> 
> On 23/11/2014 09:16, Nadav Amit wrote:
>> I’ll try to check it tomorrow (I don’t have access to the failing machine at the moment).
> 
> Thanks, you'll need to squash this in:
> 
> diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
> index 4c540c4719d8..0de1fae2bdf0 100644
> --- a/arch/x86/kernel/xsave.c
> +++ b/arch/x86/kernel/xsave.c
> @@ -738,3 +738,4 @@ void *get_xsave_addr(struct xsave_struct *xsave, int xstate)
> 
> 	return (void *)xsave + xstate_comp_offsets[feature];
> }
> +EXPORT_SYMBOL_GPL(get_xsave_addr);

I tested the patches but there are still problems.

Since kvm_load_guest_fpu is called before the guest_fpu is ever stored, there are 2 more problems that currently cause #GP:
1. XCOMP_BV[63] = 0
2. XSTATE_BV sets a bit (including bit 63) that is not set in XCOMP_BV (XCOMP_BV is initialised to zero).

[see SDM 13.11 "OPERATION OF XRSTORS”]

Once I initialise XCOMP_BV to (1ull << 63) | XSTATE_BV, the guest runs successfully.
I have not checked any other qemu functionality that might be affected by the patch.

Nadav



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