Re: [Xen-devel] [PATCH v3 1/2] x86/hvm: split all linear reads and writes at page boundary

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.03.19 at 23:30, <igor.druzhinin@xxxxxxxxxx> wrote:
> Ruling out page straddling at linear level makes it easier to
> distinguish chunks that require proper handling as MMIO access
> and not complete them as page straddling memory transactions
> prematurely. This doesn't change the general behavior.
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with one cosmetic aspect taken care of (can be done while
committing):

> @@ -1106,20 +1119,9 @@ static int linear_read(unsigned long addr, unsigned 
> int bytes, void *p_data,
>          if ( pfec & PFEC_insn_fetch )
>              return X86EMUL_UNHANDLEABLE;
>  
> -        offset = addr & ~PAGE_MASK;
> -        if ( offset + bytes <= PAGE_SIZE )
> -            return hvmemul_linear_mmio_read(addr, bytes, p_data, pfec,
> -                                            hvmemul_ctxt,
> -                                            known_gla(addr, bytes, pfec));
> -
> -        /* Split the access at the page boundary. */
> -        part1 = PAGE_SIZE - offset;
> -        rc = linear_read(addr, part1, p_data, pfec, hvmemul_ctxt);
> -        if ( rc == X86EMUL_OKAY )
> -            rc = linear_read(addr + part1, bytes - part1, p_data + part1,
> -                             pfec, hvmemul_ctxt);
> -        return rc;
> -
> +        return hvmemul_linear_mmio_read(addr, bytes, p_data, pfec,
> +                                        hvmemul_ctxt,
> +                                        known_gla(addr, bytes, pfec));
>      case HVMTRANS_gfn_paged_out:

Please retain the blank line above here (and also in the write case).

I notice that sadly the change doesn't allow removing the respective
logic from hvmemul_linear_mmio_access() yet, due to its use by
hvmemul_cmpxchg().

Jan



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