lkml.org 
[lkml]   [2020]   [Mar]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 48/70] x86/sev-es: Handle MMIO String Instructions
Date
From: Joerg Roedel <jroedel@suse.de>

Add handling for emulation the MOVS instruction on MMIO regions, as done
by the memcpy_toio() and memcpy_fromio() functions.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/kernel/sev-es.c | 78 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 78 insertions(+)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 6b0f82f81229..a040959e512d 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -415,6 +415,74 @@ static enum es_result vc_handle_mmio_twobyte_ops(struct ghcb *ghcb,
return ret;
}

+/*
+ * The MOVS instruction has two memory operands, which raises the
+ * problem that it is not known whether the access to the source or the
+ * destination caused the #VC exception (and hence whether an MMIO read
+ * or write operation needs to be emulated).
+ *
+ * Instead of playing games with walking page-tables and trying to guess
+ * whether the source or destination is an MMIO range, this code splits
+ * the move into two operations, a read and a write with only one
+ * memory operand. This will cause a nested #VC exception on the MMIO
+ * address which can then be handled.
+ *
+ * This implementation has the benefit that it also supports MOVS where
+ * source _and_ destination are MMIO regions.
+ *
+ * It will slow MOVS on MMIO down a lot, but in SEV-ES guests it is a
+ * rare operation. If it turns out to be a performance problem the split
+ * operations can be moved to memcpy_fromio() and memcpy_toio().
+ */
+static enum es_result vc_handle_mmio_movs(struct es_em_ctxt *ctxt,
+ unsigned int bytes)
+{
+ unsigned long ds_base, es_base;
+ unsigned char *src, *dst;
+ unsigned char buffer[8];
+ enum es_result ret;
+ bool rep;
+ int off;
+
+ ds_base = insn_get_seg_base(ctxt->regs, INAT_SEG_REG_DS);
+ es_base = insn_get_seg_base(ctxt->regs, INAT_SEG_REG_ES);
+
+ if (ds_base == -1L || es_base == -1L) {
+ ctxt->fi.vector = X86_TRAP_GP;
+ ctxt->fi.error_code = 0;
+ return ES_EXCEPTION;
+ }
+
+ src = ds_base + (unsigned char *)ctxt->regs->si;
+ dst = es_base + (unsigned char *)ctxt->regs->di;
+
+ ret = vc_read_mem(ctxt, src, buffer, bytes);
+ if (ret != ES_OK)
+ return ret;
+
+ ret = vc_write_mem(ctxt, dst, buffer, bytes);
+ if (ret != ES_OK)
+ return ret;
+
+ if (ctxt->regs->flags & X86_EFLAGS_DF)
+ off = -bytes;
+ else
+ off = bytes;
+
+ ctxt->regs->si += off;
+ ctxt->regs->di += off;
+
+ rep = insn_rep_prefix(&ctxt->insn);
+
+ if (rep)
+ ctxt->regs->cx -= 1;
+
+ if (!rep || ctxt->regs->cx == 0)
+ return ES_OK;
+ else
+ return ES_RETRY;
+}
+
static enum es_result vc_handle_mmio(struct ghcb *ghcb,
struct es_em_ctxt *ctxt)
{
@@ -469,6 +537,16 @@ static enum es_result vc_handle_mmio(struct ghcb *ghcb,
memcpy(reg_data, ghcb->shared_buffer, bytes);
break;

+ /* MOVS instruction */
+ case 0xa4:
+ bytes = 1;
+ /* Fallthrough */
+ case 0xa5:
+ if (!bytes)
+ bytes = insn->opnd_bytes;
+
+ ret = vc_handle_mmio_movs(ctxt, bytes);
+ break;
/* Two-Byte Opcodes */
case 0x0f:
ret = vc_handle_mmio_twobyte_ops(ghcb, ctxt);
--
2.17.1
\
 
 \ /
  Last update: 2020-03-19 10:17    [W:0.541 / U:11.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site