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Re: [PATCH 3/2] x86/pv: Rename pv.iobmp_limit to iobmp_nr and clarify behaviour
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 1 Oct 2024 15:35:38 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 01 Oct 2024 13:35:47 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01.10.2024 14:24, Andrew Cooper wrote:
> Ever since it's introduction in commit 013351bd7ab3 ("Define new event-channel
> and physdev hypercalls"), the public interface was named nr_ports while the
> internal field was called iobmp_limit.
>
> Rename the intenral field to iobmp_nr to match the public interface, and
> clarify that, when nonzero, Xen will read 2 bytes.
>
> There isn't a perfect parallel with a real TSS, but iobmp_nr being 0 is the
> paravirt "no IOPB" case, and it is important that no read occurs in this case.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with one cosmetic request:
> --- a/xen/arch/x86/pv/emul-priv-op.c
> +++ b/xen/arch/x86/pv/emul-priv-op.c
> @@ -167,7 +167,12 @@ static int guest_io_okay(unsigned int port, unsigned int
> bytes,
> if ( iopl_ok(v, regs) )
> return X86EMUL_OKAY;
>
> - if ( (port + bytes) <= v->arch.pv.iobmp_limit )
> + /*
> + * When @iobmp_nr is non-zero, Xen, like real CPUs and the TSS IOPB,
> + * always reads 2 bytes from @iobmp, which might be one byte beyond
> + * @nr_ports.
> + */
> + if ( (port + bytes) <= v->arch.pv.iobmp_nr )
If you use @nr_ports in the comment here, then I think some connection wants
establishing as to where this comes from. Otherwise use @iobmp_nr a 2nd time.
Jan
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