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Message-ID: <623a323c-943b-8c69-f877-a0669b9672dc@suse.com>
Date: Tue, 4 Oct 2022 13:03:02 +0200
From: Jan Beulich <jbeulich@...e.com>
To: Juergen Gross <jgross@...e.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 2/3] xen/pv: refactor msr access functions to support
safe and unsafe accesses
On 04.10.2022 10:43, Juergen Gross wrote:
> Refactor and rename xen_read_msr_safe() and xen_write_msr_safe() to
> support both cases of MSR accesses, safe ones and potentially GP-fault
> generating ones.
>
> This will prepare to no longer swallow GPs silently in xen_read_msr()
> and xen_write_msr().
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
Reviewed-by: Jan Beulich <jbeulich@...e.com>
Albeit ...
> @@ -933,23 +937,39 @@ static u64 xen_read_msr_safe(unsigned int msr, int *err)
> return val;
> }
>
> -static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
> +static void set_seg(unsigned int which, unsigned int low, unsigned int high,
> + int *err)
> {
> - int ret;
> - unsigned int which;
> - u64 base;
> + u64 base = ((u64)high << 32) | low;
> +
> + if (HYPERVISOR_set_segment_base(which, base) == 0)
> + return;
>
> - ret = 0;
> + if (err)
> + *err = -EIO;
... I don't see a good reason to override the error code handed to us
by the hypervisor here; I do realize though that this ...
> + else
> + WARN(1, "Xen set_segment_base(%u, %llx) failed\n", which, base);
> +}
>
> +/*
> + * Support write_msr_safe() and write_msr() semantics.
> + * With err == NULL write_msr() semantics are selected.
> + * Supplying an err pointer requires err to be pre-initialized with 0.
> + */
> +static void xen_do_write_msr(unsigned int msr, unsigned int low,
> + unsigned int high, int *err)
> +{
> switch (msr) {
> - case MSR_FS_BASE: which = SEGBASE_FS; goto set;
> - case MSR_KERNEL_GS_BASE: which = SEGBASE_GS_USER; goto set;
> - case MSR_GS_BASE: which = SEGBASE_GS_KERNEL; goto set;
> -
> - set:
> - base = ((u64)high << 32) | low;
> - if (HYPERVISOR_set_segment_base(which, base) != 0)
> - ret = -EIO;
... was this way before.
Jan
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