> -----Original Message-----
> From: Jan Beulich [mailto:jbeul...@suse.com]
> Sent: 12 September 2018 10:10
> To: xen-devel <xen-devel@lists.xenproject.org>
> Cc: Andrew Cooper <andrew.coop...@citrix.com>; Paul Durrant
> <paul.durr...@citrix.com>
> Subject: [PATCH] x86/HVM: correct hvmemul_map_linear_addr() for multi-
> page case
>
> The function does two translations in one go for a single guest access.
> Any failure of the first translation step (guest linear -> guest
> physical), resulting in #PF, ought to take precedence over any failure
> of the second step (guest physical -> host physical). Bail out of the
> loop early solely when translation produces HVMTRANS_bad_linear_to_gfn,
> and record the most relevant of perhaps multiple different errors
> otherwise. (The choice of ZERO_BLOCK_PTR as sentinel is arbitrary.)
Could we have comment perhaps saying what the order of relevance of the errors
are? The logic in update_map_err() below is a little hard to follow.
Paul
>
> Signed-off-by: Jan Beulich <jbeul...@suse.com>
>
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -531,6 +531,20 @@ static int hvmemul_do_mmio_addr(paddr_t
> return hvmemul_do_io_addr(1, mmio_gpa, reps, size, dir, df, ram_gpa);
> }
>
> +static void *update_map_err(void *err, void *new)
> +{
> + if ( err == ZERO_BLOCK_PTR || err == ERR_PTR(~X86EMUL_OKAY) )
> + return new;
> +
> + if ( new == ERR_PTR(~X86EMUL_OKAY) )
> + return err;
> +
> + if ( err == ERR_PTR(~X86EMUL_RETRY) )
> + return new;
> +
> + return err;
> +}
> +
> /*
> * Map the frame(s) covering an individual linear access, for writeable
> * access. May return NULL for MMIO, or ERR_PTR(~X86EMUL_*) for other
> errors
> @@ -544,7 +558,7 @@ static void *hvmemul_map_linear_addr(
> struct hvm_emulate_ctxt *hvmemul_ctxt)
> {
> struct vcpu *curr = current;
> - void *err, *mapping;
> + void *err = ZERO_BLOCK_PTR, *mapping;
> unsigned int nr_frames = ((linear + bytes - !!bytes) >> PAGE_SHIFT) -
> (linear >> PAGE_SHIFT) + 1;
> unsigned int i;
> @@ -600,27 +614,28 @@ static void *hvmemul_map_linear_addr(
> goto out;
>
> case HVMTRANS_bad_gfn_to_mfn:
> - err = NULL;
> - goto out;
> + err = update_map_err(err, NULL);
> + continue;
>
> case HVMTRANS_gfn_paged_out:
> case HVMTRANS_gfn_shared:
> - err = ERR_PTR(~X86EMUL_RETRY);
> - goto out;
> + err = update_map_err(err, ERR_PTR(~X86EMUL_RETRY));
> + continue;
>
> default:
> - goto unhandleable;
> + err = update_map_err(err, ERR_PTR(~X86EMUL_UNHANDLEABLE));
> + continue;
> }
>
> *mfn++ = page_to_mfn(page);
>
> if ( p2m_is_discard_write(p2mt) )
> - {
> - err = ERR_PTR(~X86EMUL_OKAY);
> - goto out;
> - }
> + err = update_map_err(err, ERR_PTR(~X86EMUL_OKAY));
> }
>
> + if ( err != ZERO_BLOCK_PTR )
> + goto out;
> +
> /* Entire access within a single frame? */
> if ( nr_frames == 1 )
> mapping = map_domain_page(hvmemul_ctxt->mfn[0]);
> @@ -639,6 +654,7 @@ static void *hvmemul_map_linear_addr(
> return mapping + (linear & ~PAGE_MASK);
>
> unhandleable:
> + ASSERT(err == ZERO_BLOCK_PTR);
> err = ERR_PTR(~X86EMUL_UNHANDLEABLE);
>
> out:
>
>
>
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